Synopsis Fresh-Water Moelusca 



Genus GYROTOMA Shuttleworth, 1845. 



37 



Shell of moderate size, spiral, clextral, imperforate, smooth 

 or spirally striate, rather thick and solid, conical or glohosely 

 ovate; aperture oval or elliptical, with a sutural slit or fissure 

 above, entire below ; lip thin and sharp. 



l^ig- 133 Type: G. ovoidca Shutt., fig. 133. Radula, fig. 134. 



Fig- 134 



Genus ANCULOSA Say, 182 1. 



Shell of moderate size, dextral, imperforate (except in one species), 

 smooth, tuberculate, spirally striate, sulcate or carinate, thick, solid, sub- 

 globose with a very short spire or thinner and conical ; aperture oval or sub- 

 circular, entire, rounded below; columella callously thickened; lip simple, 

 acute. 



Type: Afclauia prcrrosa Say, fig. 135. Radula, fig. 136. 



Fig- 135 



Fig. 136 



Order ASPIDOBRANCHIA. 



Suborder RHIPIDOGLOSSA. 



The Rhipidoglossse dififer radically from the Tsenioglossse in the charac- 

 ter of the lingual dentition. The radula has many rows of teeth, consisting 

 of a central, 2-5 laterals and numerous marginals arranged like the sticks 

 of a fan. 



Family NERITID.E. 



Head large, rostrum divided and lobed in front ; tentacles long and 

 slender; eyes carried on peduncles placed at the external base of the tenta- 

 cles ; foot large, truncate before and obtuse behind, sides simple ; gill large, 

 triangular, pointed, free at its extremity; branchial and excretory orifices 



