Uniomerus declivis - (Say, 1831)
Tapered Pondhorn
Taxonomic Status: Accepted
Related ITIS Name(s): Uniomerus declivis (Say, 1831) (TSN 80235)
Unique Identifier: ELEMENT_GLOBAL.2.827956
Element Code: IMBIV46020
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Uniomerus
Genus Size: B - Very small genus (2-5 species)
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Concept Reference
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Concept Reference: Williams, J.D., A.E. Bogan, and J.T. Garner. 2008. Freshwater Mussels of Alabama & the Mobile Basin in Georgia, Mississippi & Tennessee. University of Alabama Press: Tuscaloosa, Alabama. 908 pp.
Concept Reference Code: B08WIL01EHUS
Name Used in Concept Reference: Uniomerus declivis
Taxonomic Comments: There is much taxonomic confusion associated with southern and eastern forms of this genus. Dozens of forms of this character-poor genus have been described. This species was overlooked as a synonym in the synonomies of both Uniomerus obesus (Lea, 1831) by Clench and Turner (1956), and of Uniomerus tetralasmus (Say, 1831) by Johnson (1972). Clench and Turner (1956) erroneously stated it as Unio declivis Conrad, 1836, not Unio declivis Say, 1831. It was recognized as a distinct species by Morrison (1976), Heard (1979), and Turgeon et al. (1998); but Johnson (1999) questions whether Uniomerus declivis is merely a phenotypic variant of Uniomerus tetralasmus.

Appalachicola Basin Uniomerus have variously been recognized as Uniomerus carolinianus (e.g. Heard, 1979; Brim Box and Williams, 2000) and/or Uniomerus declivis (e.g. Heard, 1979; Davis, 1983). However, U. carolinianus may be confined to Atlantic Coast drainages and U. declivis appears to be confined to lower reaches of the Mississippi Basin (A.E. Bogan, unpublished, in Williams et al., 2008). Because of the taxonomic uncertainty, a species of Uniomerus described from the Apalachicola Basin is now recognized as Uniomerus columbensis; the earliest available name (Williams et al., 2008).
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 23Apr2007
Global Status Last Changed: 21Mar1997
Rounded Global Status: G5 - Secure
Reasons: There is considerable question as to whether this is a distinct species or a variety of Uniomerus tetralasmus. If distinct, it still occupies a large range in the southeastern U.S. west to Texas and possibly into Mexico (Great Lakes records are likely Uniomerus tetralasmus) and is stable in the core of its range.
Nation: United States
National Status: N5 (21Mar1997)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Arkansas (S2), Louisiana (S5), Mississippi (S3), Tennessee (S2), Texas (S3)

Other Statuses

American Fisheries Society Status: Currently Stable (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 5000-20,000 square km (about 2000-8000 square miles)
Range Extent Comments: Historically this species was considered a variety of Uniomerus tetralasmus. Simpson (1914) recorded it as occurring in the lower part of the Gulf states from Alabama to Louisiana. Morrison (1976), however, stated that it is "from the Lake Erie drainage, Ohio and Indiana; from Tennessee; from the Coosa River system in Alabama, and southwest across Texas to the south side of the Rio Grande system in Chihuahua, Mexico." Vidrine (1993) cites global range as the Mississippi Interior Basin, eastern Gulf and western Gulf drainages. Lower Mississipi River basin occurrences formerly attributed to Uniomerus carolinianus (e.g. Jones et al., 2005) are considered Uniomerus declivis (Williams et al., 2008).

Area of Occupancy: 2,501 to >12,500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: > 300
Number of Occurrences Comments: In Texas, this species occurs in all major drainages (Howells et al., 1996), most recently discovered for the first time in Austin Co. (Reimer and Linam, 2005). Mather and Bergmann (1994) documented it in several sites in the Cypress Bayou system (Red River drainage) in northeast Texas. In Mississippi, it occurs in the Mississippi River South, Big Black, Yazoo, Pearl, and Tombigbee drainages (Jones et al., 2005). In Louisiana, Vidrine (1993) reports this species as widespread in southwestern, central, and northern Louisiana, with isolated occurrences throughout other areas of the state. In Tennessee, it is restricted to the Hatchie River system in west Tennessee (Parmalee and Bogan, 1998). Mirarchi (2004) does not list it for Alabama, persumably subsuming it under Uniomerus tetralasmus, itself fairly common across the Gulf Coast west of the Appalachicola basin, and much of the Mobile basin. It does not, therefore, occur in Alabama with Alabama records attributable to Uniomerus tetralasmus (Williams et al., 2008). In Arkansas, it is rare in the St. Francis River (Ahlstedt and Jenkinson, 1991) and Ouachita River in Bayou Bartholomew (Mississippi Alluvian Plain) and Red River in the south central plains (Anderson, 2006). Lower Mississipi River basin occurrences formerly attributed to Uniomerus carolinianus (e.g. Jones et al., 2005) are considered Uniomerus declivis (Williams et al., 2008). McGregor et al. (1999) documented it in several sties in the Alabama River drainage (Chilatchee Creek, Hogan Creek, Cedar Creek, Dry Cedar Creek, Dry Creek), Alabama.

Population Size: >1,000,000 individuals

Number of Occurrences with Good Viability/Integrity: Unknown

Short-term Trend: Relatively Stable (<=10% change)

Long-term Trend: Decline of <30% to increase of 25%

Intrinsic Vulnerability: Not intrinsically vulnerable
Intrinsic Vulnerability Comments: This species occurs "In fine gravel in moderate current" (Heard, 1976). It may be encountered in shallow, quiet, or slow-moving water at depths seldom exceeding two feet. It is typically found buried in a substrate of fine sand and mud in shallow sloughs and ditches, and it is a species tolerant of adverse habitat conditions, surviving for periods of weeks or even months buried in the bottoms or banks of dried-up ponds (Parmalee and Bogan, 1998).

Environmental Specificity: Broad. Generalist or community with all key requirements common.
Environmental Specificity Comments: This species occurs "In fine gravel in moderate current" (Heard, 1976). It may be encountered in shallow, quiet, or slow-moving water at depths seldom exceeding two feet. It is typically found buried in a substrate of fine sand and mud in shallow sloughs and ditches, and it is a species tolerant of adverse habitat conditions, surviving for periods of weeks or even months buried in the bottoms or banks of dried-up ponds (Parmalee and Bogan, 1998).

Other NatureServe Conservation Status Information

Distribution
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Global Range: (5000-20,000 square km (about 2000-8000 square miles)) Historically this species was considered a variety of Uniomerus tetralasmus. Simpson (1914) recorded it as occurring in the lower part of the Gulf states from Alabama to Louisiana. Morrison (1976), however, stated that it is "from the Lake Erie drainage, Ohio and Indiana; from Tennessee; from the Coosa River system in Alabama, and southwest across Texas to the south side of the Rio Grande system in Chihuahua, Mexico." Vidrine (1993) cites global range as the Mississippi Interior Basin, eastern Gulf and western Gulf drainages. Lower Mississipi River basin occurrences formerly attributed to Uniomerus carolinianus (e.g. Jones et al., 2005) are considered Uniomerus declivis (Williams et al., 2008).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AR, LA, MS, TN, TX

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
AR Ashley (05003), Craighead (05031), Desha (05041), Drew (05043), Greene (05055), Jefferson (05069), Lincoln (05079), Miller (05091), Mississippi (05093), Poinsett (05111), Polk (05113), Saline (05125)
MS Bolivar (28011), Coahoma (28027), DeSoto (28033), Franklin (28037), Hinds (28049), Holmes (28051), Issaquena (28055), Itawamba (28057), Jefferson (28063), Lafayette (28071), Lauderdale (28075), Leflore (28083), Lowndes (28087)*, Monroe (28095), Newton (28101), Noxubee (28103), Oktibbeha (28105), Pearl River (28109), Quitman (28119), Rankin (28121)*, Sharkey (28125), Sunflower (28133), Tunica (28143)
TN Haywood (47075)*
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
03 Upper Tombigbee (03160101)+, Luxapallila (03160105)+*, Noxubee (03160108)+, Chunky-Okatibbee (03170001)+, Middle Pearl-Strong (03180002)+*, Lower Pearl. Mississippi (03180004)+
08 Lower Hatchie (08010208)+*, Lower St. Francis (08020203)+, Little River Ditches (08020204)+, Yocona (08030203)+, Coldwater (08030204)+, Upper Yazoo (08030206)+, Big Sunflower (08030207)+, Deer-Steele (08030209)+, Ouachita Headwaters (08040101)+, Upper Saline (08040203)+, Bayou Bartholomew (08040205)+, Boeuf (08050001)+, Lower Mississippi-Natchez (08060100)+, Lower Big Black (08060202)+, Homochitto (08060205)+
11 Mckinney-Posten Bayous (11140201)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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General Description: See Clench and Turner (1956).
Diagnostic Characteristics: Clothlike periostracum, quadrate outline, brownish to nearly black color, prominant growth lines, differs from U. CAROLINIANA (Bosc, 1801) by having a prominent postventral extension.
Reproduction Comments: This species is possibly bradytictic (long-term brooder), as Uniomerus tetralasmus appears to be (Oesch, 1984). It is stated as being dioecious, unlike the apparently parthenogenic or hermaphroditic U. tetralasmus, and of having approximately equal numbers of males and females (Morrison, 1976). Glochidial hosts are not known.
Ecology Comments: Presumably a lowland form of the Gulf coastal plain where it inhabits soft substrates of the back waters, oxbows, floodplains, palustrine forested wetlands of creeks and rivers. Like its southern congener, it may also be able to colonize temporary waters.
Habitat Type: Freshwater
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: Greatest potential during glochidial stage on fish. Adults are essentially sessile. Some passive movement downstream may occur during high flows.
Riverine Habitat(s): CREEK, Low gradient, MEDIUM RIVER, Pool
Lacustrine Habitat(s): Shallow water
Palustrine Habitat(s): FORESTED WETLAND, TEMPORARY POOL
Special Habitat Factors: Benthic
Habitat Comments: This species occurs "In fine gravel in moderate current" (Heard, 1976). It may be encountered in shallow, quiet, or slow-moving water at depths seldom exceeding two feet. It is typically found buried in a substrate of fine sand and mud in shallow sloughs and ditches, and it is a species tolerant of adverse habitat conditions, surviving for periods of weeks or even months buried in the bottoms or banks of dried-up ponds (Parmalee and Bogan, 1998).
Adult Food Habits: Detritivore
Immature Food Habits: Parasitic
Food Comments: Presumably fine particulate organic matter, primarily detritus, and/or zooplankton, and/or phytoplankton (Fuller, 1974). Larvae (glochidia) of freshwater mussels generally are parasitic on fish and there may be a specificity among some species.
Economic Attributes Not yet assessed
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Management Summary Not yet assessed
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Population/Occurrence Delineation
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Group Name: Freshwater Mussels

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on some evidence of historical or current presence of single or multiple specimens, including live specimens or recently dead shells (i.e., soft tissue still attached and/or nacre still glossy and iridescent without signs of external weathering or staining), at a given location with potentially recurring existence. Weathered shells constitute a historic occurrence. Evidence is derived from reliable published observation or collection data; unpublished, though documented (i.e. government or agency reports, web sites, etc.) observation or collection data; or museum specimen information.
Mapping Guidance: Based on the separation distances outlined herein, for freshwater mussels in STANDING WATER (or backwater areas of flowing water such as oxbows and sloughs), all standing water bodies with either (1) greater than 2 km linear distance of unsuitable habitat between (i.e. lotic connections), or (2) more than 10 km of apparently unoccupied though suitable habitat (including lentic shoreline, linear distance across water bodies, and lentic water bodies with proper lotic connections), are considered separate element occurrences. Only the largest standing water bodies (with 20 km linear shoreline or greater) may have greater than one element occurrence within each. Multiple collection or observation locations in one lake, for example, would only constitute multiple occurrences in the largest lakes, and only then if there was some likelihood that unsurveyed areas between collections did not contain the element.

For freshwater mussels in FLOWING WATER conditions, occurrences are separated by a distance of more than 2 stream km of unsuitable habitat, or a distance of more than 10 stream km of apparently unoccupied though suitable habitat. Standing water between occurrences is considered suitable habitat when calculating separation distance for flowing water mussel species unless dispersal barriers (see Separation Barriers) are in place.

Several mussel species in North America occur in both standing and flowing water (see Specs Notes). Calculation of separation distance and determination of separation barriers for these taxa should take into account the environment in which the element was collected. Juvenile mussels do not follow this pattern and juveniles are typically missed by most standard sampling methods (Hastie and Cosgrove, 2002; Neves and Widlak, 1987), therefore juvenile movement is not considered when calculating separation distance.

Separation Barriers: Separation barriers within standing water bodies are based solely on separation distance (see Separation Distance-suitable, below). Separation barriers between standing water bodies and within flowing water systems include lack of lotic connections, natural barriers such as upland habitat, absence of appropriate species specific fish hosts, water depth greater than 10 meters (Cvancara, 1972; Moyle and Bacon, 1969) or anthropogenic barriers to water flow such as dams or other impoundments and high waterfalls.
Separation Distance for Unsuitable Habitat: 2 km
Separation Distance for Suitable Habitat: 10 km
Alternate Separation Procedure: None
Separation Justification: Adult freshwater mussels are largely sedentary spending their entire lives very near to the place where they first successfully settled (Coker et al., 1921; Watters, 1992). Strayer (1999) demonstrated in field trials that mussels in streams occur chiefly in flow refuges, or relatively stable areas that displayed little movement of particles during flood events. Flow refuges conceivably allow relatively immobile mussels to remain in the same general location throughout their entire lives. Movement occurs with the impetus of some stimulus (nearby water disturbance, physical removal from the water such as during collection, exposure conditions during low water, seasonal temperature change or associated diurnal cycles) and during spawning. Movement is confined to either vertical movement burrowing deeper into sediments though rarely completely beneath the surface, or horizontal movement in a distinct path often away from the area of stimulus. Vertical movement is generally seasonal with rapid descent into the sediment in autumn and gradual reappearance at the surface during spring (Amyot and Downing, 1991; 1997). Horizontal movement is generally on the order of a few meters at most and is associated with day length and during times of spawning (Amyot and Downing, 1997). Such locomotion plays little, if any, part in the distribution of freshwater mussels as these limited movements are not dispersal mechanisms. Dispersal patterns are largely speculative but have been attributed to stream size and surface geology (Strayer, 1983; Strayer and Ralley, 1993; van der Schalie, 1938), utilization of flow refuges during flood stages (Strayer, 1999), and patterns of host fish distribution during spawning periods (Haag and Warren, 1998; Watters, 1992). Lee and DeAngelis (1997) modeled the dispersal of freshwater into unoccupied habitats as a traveling wave front with a velocity ranging from 0.87 to 2.47 km/year (depending on mussel life span) with increase in glochidial attachment rate to fish having no effect on wave velocity.

Nearly all mussels require a host or hosts during the parasitic larval portion of their life cycle. Hosts are usually fish, but a few exceptional species utilize amphibians as hosts (Van Snik Gray et al., 2002; Howard, 1915) or may metamorphose without a host (Allen, 1924; Barfield et al., 1998; Lefevre and Curtis, 1911; 1912). Haag and Warren (1998) found that densities of host generalist mussels (using a variety of hosts from many different families) and displaying host specialists (using a small number of hosts usually in the same family but mussel females have behavioral modifications to attract hosts to the gravid female) were independent of the densities of their hosts. Densities of non-displaying host specialist mussels (using a small number of hosts usually in the same family but without host-attracting behavior) were correlated positively with densities of their hosts. Upstream dispersal of host fish for non-displaying host specialist mussels could, theoretically, transport mussel larvae (glochidia) over long distances through unsuitable habitat, but it is unlikely that this occurs very often. D. Strayer (personal communication) suggested a distance of at least 10 km, but a greater distance between occurrences may be necessary to constitute genetic separation of populations. As such, separation distance is based on a set, though arbitrary, distance between two known points of occurrence.

Date: 18Oct2004
Author: Cordeiro, J.
Notes: Contact Jay Cordeiro (jay_cordeiro@natureserve.org) for a complete list of freshwater mussel taxa sorted by flow regime.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 23Apr2007
NatureServe Conservation Status Factors Author: Cordeiro, J.
Element Ecology & Life History Edition Date: 23Apr2007
Element Ecology & Life History Author(s): Cordeiro, J. (2007); BUTLER, R.S. (1992)

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Ahlstedt, S.A. and J.J. Jenkinson. 1991. Distribution and abundance of Potamilus capax and other freshwater mussels in the St. Francis River system, Arkansas and Missouri, U.S.A. Walkerana, 5(14): 225-261.

  • Brim Box, J. and J.D. Williams. 2000. Unionid mollusks of the Apalachicola Basin in Alabama, Florida, and Georgia. Alabama Museum of Natural History Bulletin, 21: 1-143.

  • Clench, W.J. and R.D. Turner. 1956. Freshwater mollusks of Alabama, Georgia, and Florida from the Escambia to the Suwanee River. Bulletin of the Florida State Museum Biological Sciences, 1(3): 97-239.

  • Fuller, S.L.H. 1974. Chapter 8: Clams and mussels (Mollusca: Bivalvia). Pages 215-273 in: C.W. Hart, Jr. and S.L.H. Fuller (eds.) Pollution Ecology of Freshwater Invertebrates. Academic Press: New York. 389 pp.

  • Heard, W.H. 1979. Identification manual of the fresh water clams of Florida. State of Florida, Department of Environmental Regulation, Technical Series, 4(2): 1-82.

  • Johnson, R.I. 1972a. The Unionidae (Mollusca: Bivalvia) of peninsular Florida. Bulletin of the Florida State Museum of Biological Science 16(4): 181-249.

  • Johnson, R.I. 1972b. Bibliography in: The Unionidae (Mollusca: Bivalve) of Peninsular Florida. Bulletin of the Florida State Museum Biological Sciences 16 (4):244-247.

  • Johnson, R.I. 1999. Unionidae of the Rio Grande (Rio Bravo del Norte) system of Texas and Mexico. Occasional Papers on Mollusks, 6(77): 1-65.

  • McGregor, S.W., T.E. Shepard, T.D. Richardson, and J.F. Fitzpatrick, Jr. 1999. A survey of the primary tributaries of the Alabama and Lower Tombigbee rivers for freshwater mussels, snails, and crayfish. Geological Survey of Alabama, Circular 196. 29 pp.

  • Mirarchi, R.E., et al. 2004a. Alabama Wildlife. Volume One: A Checklist of Vertebrates and Selected Invertebrates: Aquatic Mollusks, Fishes, Amphibians, Reptiles, Birds, and Mammals. University of Alabama Press: Tuscaloosa, Alabama. 209 pp.

  • Morrison, J.P.E. 1976. Species of the genus Uniomerus. Bulletin of the American Malacological Union, 1976: 10-11.

  • Oesch, R.D. 1984a. Missouri Naiades: a Guide to the Mussels of Missouri. Jefferson City, Missouri: Conservation Commision of the State of Missouri. 270 pp.

  • Parmalee, P.W. and A.E. Bogan. 1998. The Freshwater Mussels of Tennessee. University of Tennessee Press: Knoxville, Tennessee. 328 pp.

  • Parmalee, P.W. and A.E. Bogan. 1998. The freshwater mussels of Tennessee. University of Tennessee Press, Knoxville, Tennesee. 328 pp.

  • Reimer, M.M. and L.A. Linam. 2005. Texas mussel watch, a citizen based volunteer monitoring program. Ellipsaria, 7(3): 5-6.

  • Simpson, C.T. 1914. A Descriptive Catalogue of the Naiades or Pearly Fresh-water Mussels. Bryant Walker: Detroit, Michigan. 1540 pp.

  • Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and J.D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland: 526 pp.

  • Williams, J. D., A. E. Bogan, R. S. Butler, K. S. Cummings, J. T. Garner, J. L. Harris, N. A. Johnson, and G. T. Watters. 2017. A revised list of the freshwater mussels (Mollusca: Bivalvia: Unionida) of the United States and Canada. Freshwater Mollusk Biology and Conservation 20:33-58.

  • Williams, J.D., A.E. Bogan, and J.T. Garner. 2008. Freshwater Mussels of Alabama & the Mobile Basin in Georgia, Mississippi & Tennessee. University of Alabama Press: Tuscaloosa, Alabama. 908 pp.

  • Williams, J.D., M.L. Warren, Jr., K.S. Cummings, J.L. Harris, and R.J. Neves. 1993b. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9): 6-22.

References for Watershed Distribution Map
  • Howells, R.G., R.W. Neck, and H.D. Murray. 1996. Freshwater Mussels of Texas. Texas Parks and Wildlife Press: Austin, Texas. 218 pp.

  • Jones, R.L., W.T. Slack, and P.D. Hartfield. 2005. The freshwater mussels (Mollusca: Bivalvia: Unionidae) of Mississippi. Southeastern Naturalist, 4(1): 77-92.

  • Mather, C.M., and J.A M. Bergmann. 1994. Freshwater mussels of the Cypress Bayou system, northeast Texas. Malacology Data Net, 3(5/6): 139-145.

  • Vidrine, M.F. 1993. The Historical Distributions of Freshwater Mussels in Louisiana. Gail Q. Vidrine Collectibles: Eunice, Louisiana. xii + 225 pp. + 20 plates.

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