578 



MOLLUSCA 



2.5 mm. wide: Cape Cod to Texas; common in shallow water; West 

 Indies. 



FAMILY 4. CYPRINIDAE. 



Shell regular, equivalve, more or 

 less oval, thick, with a thick periostra- 

 cum; ligament external; pallial line sin- 

 uous; both siphons complete: numerous 

 species. 



CYPEINA Lamarck. Umbo nearly 

 central, directed towards the forward 

 end ; hinge with 3 diverging cardinal teeth 

 and a posterior lateral in each valve ; foot 

 thick: 1 species on the Atlantic coast. 



C. islandica (L.) (Fig. 909). Shell 

 thick, coarsely wrinkled, 80 mm. long, 75 mm. high, and 45 mm. wide, 

 dark colored : Long Island to the Arctic Ocean, in rather deep water, but 

 often thrown UD on the beach; Europe. 



Fig. 909 Cyprina islandica 

 (Gould). 



FAMILY 5. UNIONIDAE.* (NAIADES.) 



Fresh-water clams or mussels. Shell equivalve, with a thick pearly 

 layer and a dark-colored periostracum ; umbo towards the anterior end; 

 ligament external and ^ 



prominent; hinge teeth j tt 



consisting of cardinals and 

 posterior laterals (Fig. 

 910), present or not; anal 

 siphon complete but very 

 short; foot large, with 

 byssus only in the young: 

 cosmopolitan; about 1,000 

 species, of which over 500 

 occur in this country, all 

 living in fresh-water 

 streams and ponds; some 

 are used for food, and the 



Fi 



ig. 

 eol 



910 Diagram of the left valve of Lampsilis 

 luteolus (Baker). 1, posterior adductor muscle 

 scar ; 2, posterior foot retractor muscle scar ; 3, 

 posterior lateral teeth ; 4, ligament ; 5, umbo ; 

 6, lunule ; 7, anterior adductor muscle scar ; 8. 

 cardinal teeth ; 9, anterior foot retractor muscle 

 scar ; 10, pallial line. 



* See "Observations on the Genus Unio with Descriptions of New Species," by 

 I. Lea, 13 vols., Philadelphia, 1834-1874. "Synopsis of the Naiades or Pearly Fresh- 

 water Mussels," by C. T. Simpson, Proc. U. S. Nat. Mus., Vol. 22, p. 501, 1900. "A 

 Preliminary List of the Unionidae of West. Penn.," etc., by A. E. Ortmann, Ann. 

 Cam. Mus., Vol. 5, 1909. "Notes upon the Families and Genera of the Naiades," 

 byname, same jour., Vol. 8, 1912. "Notes on the Unionidae and Their Classification," 

 by V. Sterki, Am. Nat., Vol. 37, p. 103, 1903. "Studies on the Reproduction and 

 Artificial Propagation of Fresh-water Mussels," by G, Lefevre and W, C, Curtis, Bull. 

 Bur. Fish., Vol. 30, p. 105, 1912. 



