POLYGYRELLA. 



289 



Fig. 186. 



Jaw of. P. polygyrella. 



POLYGYRELLA, BLAND. 



Animal heliciform ; mantle subcentral ; other characters as in Patula. 



Shell widely umbilicated, discoidal, 

 ribbed above, smoother below ; whorls 7-8, 

 gradually increasing, the last deflected 

 above, furnished within with two rows of 

 three teeth ; base flattened, umbilicus of 

 equal size to the apex ; aperture subver- 

 tical, oblique, lunate-oval ; peristome white, 

 simple, much thickened within, margins joined by a white, pliciforni, elevated, 

 triangular tooth. 



Central Province ; a single species known. 



Jaw of the only known species, P. polygyrella, very low, wide, very slightly 

 arcuate, ends very gradually attenuated : cutting margin without median pro- 

 jection : anterior surface with numerous (even 26), broad, slightly separated 

 ribs, denticulating either margin. 



Lingual membrane (PI. VII. Fig. A) long and narrow. Teeth 27 1 27, 

 with 5 perfect laterals. Centrals subquadrate, the lower lateral angles but 

 little expanded ; the upper margin broadly reflected : reflection large, wide, 

 with distinct, but small, rounded side cusps bearing short conical cutting points, 

 and a very stout median cusp reaching the lower margin of the base of attach- 

 ment, beyond which projects the short, stout, conical cutting point. Laterals 

 like the centrals, but asymmetrical by the suppression of the inner, lower 

 angle of the base of attachment, and the inner side cusp and cutting point. 

 First marginals a simple modification of the laterals by the lesser development 

 of the cutting point (6). Outer marginals (c) low, wide, the reflection equal- 

 ling the base of attachment and bearing one inner, short, stout, oblique cutting 

 point, and two shorter outer blunt cutting points. 



Polygyrella is quite distinct from all the other American genera by the form 

 of its jaw and the large number of ribs upon its anterior surface. 



Fig. 187. 



Polygyrella polygyrella, BLAND. 



Shell widely umbilicate, discoidal, flat, shining, translucent, yellowish horn- 

 colored, ribbed above, the ribs obsolete near the aperture, base rather smooth ; 

 spire scarcely elevated ; whorls 7 to 8, somewhat convex, gradu- 

 ally increasing, the last slightly deflexed above, armed within 

 with two rows of three teeth, seen through the outer wall ; um- 

 bilicus pervious, of equal size to the apex ; aperture subvertical, 

 oblique, lunate-oval; peristome depressed above, white, simple, 

 much thickened within, the margins joined by a white, pliciforni, 

 elevated, triangular tooth. Greater diameter ll, lesser 

 mill. ; height, 5 mill. 



VOL. IV. 19 



P. polygyrella. 



