68 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



Genus Polygyra, Say. 



A large genus divided into three sections, all confined to North 

 America. The first section, Polygyra, s.s., has about fifty species. 

 P. cereolus, Muhlf., and P. septemvolva, Say, are characterized by 

 a raised parietal callus, with an oblique, entering fold and a scrobicu- 

 lationbehind the peristome. P. espiloca, Bid., and P. auriformis, Bid., 

 have in addition a transverse fold on the outer lip and a horizontal 

 one on the lower lip of the peristome. P. uvulifera, Shutt., and 

 P. auriculata, Say, have a similar armature, but more produced, 

 the raised parietal plate is more tortuous and tongue-shaped and 

 projects between the plates on the peristome almost closing the 

 aperture. P. hippocrepis, Pfr., possesses an extraordinary form of 

 armature, having the raised parietal callus provided with two 

 parallel, horizontal entering laminae united at their inner termina- 

 tion by a high raised, curved, transverse fold, in the shape of a horse- 

 shoe, which coincides with a hollow, raised, transverse tubercle on the 

 base of the outer wall near the scrobiculation behind the peristome. 



The section Triodopsis, Raf., also contains about fifty species, 

 with numerous varieties. Here the armature is less complicated, 

 and in some forms altogether absent, but the peristome in all is 

 strongly developed. P. tridentata, Say, and P. fraudulenta, Pils., 

 have one oblique, entering fold on the parietal callusand two denticles 

 on the peristome, one above and one below, while P. profunda, Say, 

 is provided merely with a denticle on the basal margin of the 

 peristome. P. Sayi, Binn., and P. elevata, Say, have an oblique 

 entering denticle or fold on the parietal callus, whereas P. albolabris, 

 Say, P. muUilineata, Say, and P. clausa, Say, are devoid of any 

 teeth, folds, or lamellae whatever. 



The section Stenotrema, Raf., numbers some twenty-two 

 species, the majority having the aperture nearly closed by the 

 raised, transverse lamella on the parietal wall. In P. spinosa, 

 Lea, this lamella has the distal end curved inwardly, fitting 

 into the upper angle formed by the upper and outer margins 

 of the peristome, which is considerably thickened ; in addition an 

 internal short buttress unites a part of the j)arietal and basal walls 

 with the columellar wall, one-quarter of a whorl behind the peristome, 

 this buttress being distinctly visible through the shell -wall, but can 

 be more easily observed on breaking away a portion of the lower 

 shell- wall, immediately behind the peristome. P. labrosa, Bid., and 

 P. stenotrema, Per., have the aperture still more obstructed. In these 

 two species the basal margin of the peristome is inwardly produced 

 with a small sinus near the distal end, and the outer margin carries 

 a short tubercle, forming a sinus with the basal margin, into which 

 the distal end of the parietal plate fits. P. monodon, Rack., and 

 P. fraterna. Say, have a less complicated armature, being furnished 

 simply with the raised, transverse lamella on the parietal plate, 

 no processes occurring on the peristome. 



