EASTERN PROVINCE SOUTHERN REGION SPECIES. 



3G1 



By the character of its jaw Polygyra can be coin[)are(l only to Tri- 

 odopsis and Mesodon among the other North American genera of disin- 

 tegrated Helix. No foreign species has yet been examiued. 



Fig. 392 shows the general arrangement of the teeth upon the lingual 

 membrane, the characters of the individual teeth being better shown 

 in my Plate VI of Terr. Moll., V, and also in Fig. 11, on p. 50. 



Flc. :i9J 





mmmmmA 



Lingual dentition of P. auriformix? (Leidy.) 



The teeth do not differ from what I have described under Sfeno- 

 trema (see above). As in all the subgenera, there is considerable differ- 

 ence in the length of the base of attachment on the central and lat- 

 eral teeth in the several species. 



I find considerable difference between the various species in the man- 

 ner in which the lateial teeth pass into the niarginnls. In aurifor- 

 mis, Postelliana, cspiloca^ and Hazardi the change is made simply by 

 the greater development of the inner cutting point, not by ite bifur- 

 cation (see Terr. Moll., Y, Plate VI, Fig. N). In these species it is 

 only the extreme outer marginals that have their inner cutting point 

 bifid; in auriformis a very few extreme marginals have a bifid cutting 

 point. This species has very long inner cutting points to its marginal 

 teeth. In the other species examined by me the first marginals have 

 their inner cutting point bifid, the transition from laterals to marginals 

 being thus very distinctly marked (see Terr. Moll., V, Plate VI, Fig. 

 K). With these exceptions the dentition of our species of Polygyra 

 is v^ery like that of Stetwtrema {q. v.). 



The dentition of no foreign species is known witli which to compare 

 that of our species. 



PoSyuyrsi aiii'iciilala. Say. 



Shell rimately perforated, thittened above, iiitlated below, with rib- 

 like strife, reddish horn-color or brownish; whorls 5^, ^i«- 393. 

 narrow^ the last deflected at the aperture, disjoined, 

 constricted and scrobiculated below ; umbilicus level, 

 showing only the penultimate whorl; aperture subhor- 

 izontal, ear-shaped, ringent, almost closed ; peristome 

 continuous, its terminations joined by an oblong, en- 

 tering, excavated fold, the right margin furnished within with a deep 



