1896.] NATURAL SCIENCES OF PHILADELPHIA. 19 



constricted behind the outer and basal lips. Suture slightly im- 

 pressed, rather abruptly and deeply deflexed in front. 



Aperture oblique, oblong, the upper and basal margins subparal- 

 lel ; outer lip reflexed, its inner edge bearing a concave lamina 

 ending below in a denticle ; basal lip reflexed, impinging on the 

 umbilicus, with a compressed tooth separated from the lamella on 

 outer lip by a deep squarish sinus, a gentle swelling to the left of it. 

 Parietal wall glazed with a translucent film, and bearing a long V- 

 shaped tooth, the outer branch of which is short and not connected 

 with the upper insertion of outer lip. 



Alt. 5*5, greatest diam. 85, lesser 7'5 mm. 



Type in collection of Mr. John Ponsonby of London. It is said 

 to be from Mexico, and has the appearance of a northern Mexican 

 shell. 



The strong, whitish rib-strise, narrow and nearly regular umbilicus 

 with spiral groove within on the last whorl, and the aperture much 

 as in euglypta, Riehardsoni and ventrosula, are a combination of 

 characters amply sufficient to distinguish this species from other 

 forms now known ; and while I am opposed on principle to the 

 description of species without exact locality record, it seems best in 

 some cases to depart from this salutary rule. I do not think any one 

 will have difficulty in recognizing the species, as no other Polygyra 

 having the apertural characters of this one, presents a similar um- 

 bilicus or sculpture. 



EXPLANATION OF PLATES II and III. 



Polygyra Ponsonbyi n. sp., seen from below. 

 Polygyra Ponsonbyi n. sp., anterior view. 

 Polygyra Ponsonbyi u. sp., aperture, the plane of peri- 

 stome at a right angle to line of vision, 

 Polygyra albicostulata n. sp., from below. 

 Polygyra albicostulata n. sp., anterior view. 

 Polygyra albicostulata n. sp., aperture, the plane of peri- 

 stome at a right angle to line of vision. 

 Fig. 7. Polygyra euglypta n. sp., aperture, the plane of peristome 



at right angle to line of vision. 

 Fig. 8. Polygyra euglypta n. sp., seen from below. 

 Fig. 9. Polygyra euglypta n. sp., anterior view. 

 Fig. 10. Polygyra matermontana n. sp., anterior view. 

 Fig. 11. Polygyra matermontana n. sp., seen from above. 



