CHAPTER XV: THE CYRENAS AND PEA SHELLS 



Family Cyrenid^ 



Shell equivalve, sub-triangular, small; hinge with two or 

 three cardinals, and laterals; surface smooth, with periostracum; 

 foot large, without byssus; siphons short. Sexes united in the 

 individual; reproduction viviparous. Active bivalves, living in 

 fresh or brackish water, believed to be derived from the marine 

 family, Veneridce. 



Genus CYRENA, Lam. 



The Southern Cyrena (C. Carolinensis, Bosc.) looks like a 

 Mactra, but has two and three divergent cardinal teeth to form 

 the hinge, with no pit such as the surf clams have. The smooth, 

 ventricose valves are covered with a shining, brittle epidermis, 

 usually rubbed off at the umbones. The beaks curl over the 

 hinge line in quite pointed hooks. 



These mollusks inhabit the muddy bottoms of brackish 

 water on sub-tropical coasts. Length, 2 or 3 inches. 



Habitat. — Georgia to Texas and West Indies. 



Genus SPHiERIUM, Scop. 



Shell small, oval, oblique; hinge strong; siphons separate; 

 foot mobile, used in climbing, and as a pond snail uses its foot 

 in floating suspended at the surface of ponds. The clam also 

 spins a mucus thread to travel on from place to place among 

 stems of submerged water plants. The young remain in the 

 brood pouch until able to take care of themselves; they are then 

 shot out through the siphon. 



The Furrowed Sphere Shell {S. sulcatum, Lam.) looks like 

 a tiny model of a Venus clam, as it is obliquely oval with beaks 

 well forward. The mollusk is found in still water, often climbing 

 submerged plants, and waving its two siphon tubes while the 



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