PELECYPODA 579 



shells of many of the thick-shelled species are manufactured into buttons. 

 The eggs are carried usually in the outer pair of gills until the young 

 larvae, which are called glochidia, are hatched. These attach them- 

 selves, except in Strophitus, to the skin of fishes, in which they become 

 encysted, and there complete their development. 



Key to the genera of Unionidae here described: 



Ci Hinge teeth (Fig. 910) well developed; shell usually thick. 

 61 Shell with distinct raj^s radiating from the umbo (Fig. 911) . .1. Lampsilis 

 6, No distinct rays. 



c, Shell elongate G. Unio 



c. Shell quadrate 8. Quadrula 



O3 Hinge teeth absent or rudimentary ; shell thin. 

 hi Teeth absent. 



Ci Hinge line not incurved in front of umbo 3. Anodonta 



Ca Hinge line incurved 7. Anodontoides 



5, Teeth incomplete or rudimentary. 



Ci Shell elongate, reniform 5. Margaritana 



Cj Shell rhomboid or round. 



di Teeth rudimentary 2. Strophitus 



da Cardinals present, laterals blurred 4. Alasmidonta 



1. Lampsilis Rafinesque. Shell oval or elliptical, usually thick, 

 with a hard, bright, usually rayed periostracum ; hinge with 2 cardinals 

 (Fig. 910, 8) and 2 (posterior) laterals in the left and usually 1 of each 

 in the right valve; male and female sexually dimorphic, the female shell 

 being swollen at the base just behind the middle: 128 species, all 

 American. 



Key to the species of Lampsilis here described: 



Oi Length not twice the height. 

 61 Length one-third greater than the height. 

 Ci Cardinals strong and prominent. 

 di Shell compressed. 



Ci Umbo and rays prominent L. radiata 



€2 Umbo and rays not prominent L. ligamentina 



dj Shell very wide L. ventricosa 



c. Cardinals weak L. gracilis 



ftj Length nearly twice the height. 



Ci Shell large and thick L. luteola 



Cj Shell small and compressed " L. iris 



Cj Length about 21/^ times the height. 



6, Color black L. recta 



6, Color yellow L. anodontoides 



L. radiata (Gmelin) (Fig. 911). Shell ovate, somewhat angular 

 posteriorly, umbo at the anterior fourth; surface with numerous rays of 

 dusky green ; length 75 mm. ; height 42 mm. ; breadth 30 mm. : Atlantic 

 slope, south to North Carolina; northerly to St. Lawrence slope; west 

 to Manitoba; common. 



