THE MOLLUSCA 



991 



85 (86) Shell obliquely ovate, thick, solid, imperforate; columella flattened 

 and calloused; lip sinuous, effuse, and projecting anteriorly. 

 Verge winged ... Fluminicola Stimpson. 



A characteristic west coast genus. In shell characters, it is quite simi- 

 lar to Somatogyrus, but differs radically in anatomical details and is widely 

 separated in range. Type, F. nultaUiana Lea (Fig. 1464; X 2). 



Fig. 1465. 



Fig. 1464. 



86 (87) Shell usually thick and sohd, imperforate or narrowly perforate; 

 body- whorl large; columella callously thickened; spire usu- 

 ally short; aperture very oblique, lip projecting above; oper- 

 culum subspiral, nuclear whorls small, rapidly increasing. 



Somatogyrus Gill. 



A group of small species found, mainly, south of the Ohio and east of the 

 Mississippi. The thickened columella is characteristic and enables the species 

 to be easily separated from the associated genera. Example, 5. subglobosus 

 Say (Fig. 1465; X2). 



87 (86) Shell not very thick, imperforate; body- whorl large; spire short; 

 peritreme continuous in the same plane; columella scarcely 

 thickened. Verge simple Gillia Stimpson. 



This genus is restricted to the Atlantic coast states, ranging from New Jer- 

 sey to South Carolina. Type, G. aitilis Lea (Fig. 1466; x 2). 



Fig. 1466. 



88 (89) Shell as in Amnicolinae, very small; operculum circular, multispiral. 



Foot simple Subfamily Lyogyrinae. 



Only one genus Lyogyrus Gill. 



A peculiar genus of minute species restricted to the Atlantic coast states. 

 Easily distinguished by its operculum. Type, L. pupoideus Gld. (Fig. 1467; x6). 



Fig. 1467. 



89 (88) Shell elevated, turreted; operculum subspiral. Foot divided by a 



transverse sulcus Subfamily Pomatiopsinae. 



Only one genus Pomatiopsis Tryon. 



The species of this group are terrestrial or rather semiamphibious in habit, 

 being always found near but not in the water. The divided foot is very pe- 

 cuUar. The animal, aided by its long snout, progresses by a series of steps. 

 Type, P. lapiiaria Say (Fig. 1468; X 4)- 



Fig. 1468. 



90 (72) Shell dextral, spiral, thick, solid, globose, or elongated; operculun. 

 corneus, subspiral. Animal without an external verge. Cen- 

 tral tooth of the radula without basal denticles. 



Family Pleuroceratidae . . 91 

 Seven genera: 91, 92, 94, gs, 97. 98, 99- 



