584 . MOLLUSCA 



Key to the species of Quadrula here described: 



Ci Shell elliptical. 



61 Shell smooth Q. rubiginosa 



5j Shell coarsely wrinkled Q. undulata 



a. Shell round Q, pustulosa 



Q. rubiginosa (Lea). Shell elliptical, thick, compressed, dark yellow 

 in color ; umbo marked with 5 or 6 heavy ridges ; cardinals double in both 

 valves; 7 cm. long; 6 cm. high, and 3 cm. wide: valleys of the Mississippi 

 and St. Lawrence. 



Q. undulata (Barnes). Blue foot (Fig. 919). Shell squarish, com- 

 pressed, very thick and heavy; umbo marked by 5 coarse diverging 

 3 ridges; cardinals double in both valves; 



length 15 cm. ; height 10 cm. ; width 6 cm. ; 

 ^1 p,2Sj^r ji\ color brown or black: valleys of Missis- 



}[ I sippi and St. Lawrence ; also Gulf slope ; 

 common; used for button-making. 



Q. pustulosa (Lea). Shell round, in- 

 flated, thick, and heavy, 59 mm. long and 

 Fig. 919~Quadrula undulata lii§'h and 36 mm. wide, yellowish-brown in 

 (ilTe^K'Y/L7eraL!'2%rr(U- color, with a broad band of dark green 

 nals ; 3, umbo. ' ' extending from the umbo to the ventral 



border; cardinals double in both valves: Mississippi valley; Michigan; 

 Gulf slope. 



Family 6. DKEISSENSIIDAE. 



Shell like Mytilus without its pearly lining; umbo at the interior 

 end ; mantles fused below, with both siphons complete and prominent ; 

 foot small, with byssus : 2 genera ; marine. 



CoNGERiA Partsch. With the characters of the family: several 

 species. 



D. leucophseta (Conrad). Shell 13 mm. long, 7 mm. high, 6 mm. 

 wide; outer surface rough and brownish: Maryland and southwards, on 

 oysters in brackish water. 



Family 7. LUCINIDAE. 



Shell round, equivalve, compressed ; anterior muscle impression nar- 

 rower and much longer than the posterior; foot very long, without 

 byssus; mantle open below; siphons usually incomplete; ligament more 

 or less internal: 200 species. 



Key to the genera of Lucinidae here described: 



tti Hinge teeth present 1. Lucina 



a. No teeth 2. Cryptodon 



