The mollusca 



1015 



160 (161) Male and female shells alike ; very thick and solid, inflated, rounded- 

 triangular; surface nodular, radiately wrinkled, or lachry- 

 mous; epidermis painted with dehcate green mottling on a 

 light ground. Marsupium consisting of several long purple 

 ovisacs pendent from near the central base of the outer 

 gills and formed into a close coil with the ends turned inward. 



Cyprogenia Agassiz. 



The typical species, C. irrorala Lea (Fig. 1,522), is common in the Ohio, Cumberland, and 

 Tennessee river systems. One other species occurs in the states west of the Mississippi, from 

 Missouri to Oklahoma. 



I'lG. 1522. 



161 (162) Male and female shells different, that of the latter being slightly 

 swollen behind the middle of the base. Shell rather small, 

 elongated, dorsal slope plicately or nodulously wrinkled; 

 hinge complete. Marsupium occupying the central portion 

 of the outer gill Medionidus Simpson. 



A small group of species characterized by their elongate shape and plicate dorsal slope. It 

 is restricted to the waters of Tennessee, Alabama, Georgia, and Florida. Type, M. conradicus 

 Lea (Fig. 1523). 



Fig. 1523. 



