The Pearly Fresh-water Mussels 



U. spinosus, Lea, is an isolated species, distinguished by 

 sharp thorn-like spines, one or two on each valve, near the beak. 

 It is found in the Altamaha River, Georgia. 



U. gibbosus, Barnes, is a mid-continental Unio of wide 

 distribution. The shell is solid, triangularly or elongately ovate, 

 arcuate when old, gibbous above, rounded in front, pointed or 

 biangulate behind, with a moderate posterior ridge; beaks low, 

 sculptured with a few strong, parallel ridges; epidermis cloth-like, 

 dull; hinge teeth strong, rough; laterals club-shaped, vertically 

 striated or granular; one or more furrows and ridges run parallel 

 to laterals; muscle scars distinct, deep; mantle thin, with thick- 

 ened edges ; gills large, curved at ventral border. Several varieties 

 are recognised. Length, 3 to 5 inches. 



Habitat. — Entire drainage areas of St. Lawrence, Mississippi 

 and Alabama Rivers; also to Guadaloupe River, Texas, and into 

 Florida. 



Genus ANODONTA, Lam. 



Shell thin, elliptical, often slightly winged posteriorly, in- 

 flated; beaks with fine parallel ridges, sometimes looped and nodu- 

 lous; hinge toothless, reduced to a curved line; surface smooth, 

 shining; pearl dull. Sexes with shells alike; marsupia filling 

 whole of outer gills. 



The Swan Mussel (A. cygnea, Linn.) is spread over Europe 

 and Siberia. Its synonyms are legion, owing to its variability, 

 and the tendency of "new school" conchologists to give slight 

 variations the rank of specific characters. 



A. grandis, Say, is a large and widely distributed American 

 species. It inhabits the entire Mississippi system, the St. Law- 

 rence and Red River of the North, Lake Winnipeg, Manitoba, 

 extending to Southeastern Pennsylvania and into Texas. 



A. marginata, Say, is a fragile, elongated Anodonta, with 

 green epidermis, and bluish white lining, found in the St. Law- 

 rence drainage. 



Genus LAMPSILIS, Raf. 



Shell oval or elliptical, usually smooth, without posterior 

 ridge; epidermis shiny, often brilliantly rayed; two hinge teeth 



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