584 MOLLUSCA 



Key to the species of Quadrula here described: 



0j Shell elliptical. 



6j Shell smooth Q. BUBIGINOSA 



6, 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 



ridges; cardinals double in both valves; 

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

 color brown or black: valleys of Missis- 

 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 

 ni g h and 36 mm - wide > yellowish-brown in 

 color, with a broad band of dark green 

 extending from the umbo to the ventral 

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

 Gulf slope. 



FAMILY 6. DEEISSENSIIDAE. 



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. leucophaeta (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: 



o t Hinge teeth present 1. LUCINA 



o a No teeth 2. CRYPTODON 



