PELECTPODA 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: 



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

 6j hell with distinct rays radiating from the umbo (Fig. 911) . .1. LAMPSILIS 

 6, No distinct rays. 



c x Shell elongate 6. UNIO 



c. Shell quadrate 8. QUADRULA 



a, Hinge teeth absent or rudimentary ; shell thin. 

 &! Teeth absent. 



G! Hinge line not incurved in front of umbo 3. ANODONTA 



c a Hinge line incurved 7. ANODONTOIDES 



Z>, Teeth incomplete or rudimentary. 



Cj Shell elongate, reniform 5. MARGABITANA 



c a Shell rhomboid or round. 



</! Teeth rudimentary 2. STROPHITUS 



d. 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: 



a^ Length not twice the height. 

 &! Length one-third greater than the height. 

 Cj Cardinals strong and prominent. 

 dt Shell compressed. 



d Umbo and rays prominent L. RADIATA 



e 2 Umbo and rays not prominent L. LIGAMENTINA 



d 2 Shell very wide L. VENTRICOSA 



c, Cardinals weak L. GRACILIS 



ft. Length nearly twice the height. 



c t Shell large and thick L. LUTEOLA 



Cj Shell small and compressed L. IRIS 



a. Length about 2 1 / times the height. 



&! Color black L. RECTA 



& a 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. 



