72 



POLYGYRA. 



Bermudas, Bahamas and Cuba. Most species, such as cereolus, aurifor- 

 mis, mooreana, etc. are gregarious, and occur in great numbers. All 

 are ground snails, living at the roots of grass, or under bits of wood 

 or leaves ; and while some forms such as auriformis are found only 

 in the immediate proximity of water, others occur in very dry situa- 

 tions, the arid mesquite chaparral of southern Texas being inhabited 

 by texasiana and mooreaim. 



Species without teeth on the outer lip. 



Bland has published an excellent essay upon these forms in 

 Annals N. Y. Lyceum vii, 132, 1860, but his material was not 

 extensive enough to show the intermediate forms now known. The 

 forms included under P. cereolus are absolutely connected by a series 

 of transitions, in which the supposed specific characters found in the 

 striation or ribbing, the degree of carination, number of whorls, form 

 of umbilicus and presence or absence of an internal lamina, blend 

 by imperceptible degrees. 



The typical cereolus is found on the Florida keys and adjacent 

 mainland ; it passes into the smaller form carpenteriana, which con- 

 tinues up the coast, mainly westward ; occurring also at Matanzas, 

 Cuba ! In central and eastern Florida xeptemvolva occurs, its small 

 race volvoxis spreading north to St. Simon's I., Georgia, and to the 

 west (tinder the name febigeri) it occurs at New Orleans, La., and 

 Galveston, Texas. Var microdonta, which is typically quite distinct 

 in its fine striation, occurs abundantly in Bermuda, and also on New 

 Providence (at Nassau), Bahamas. At the latter locality transition 

 forms occur; and it must also be noted that some specimens of 

 volvoxis from Florida (Tampa) and carpenteriana (Key Biscayne) 

 show striation equally fine. Species of this group inhabit the neigh- 

 borhood of the sea, and generally occur in great numbers. Besides 

 the species enumerated below there is another Polygyra with tooth- 

 less outer lip, P. anilis ; but its relationships are with an entirely 

 different group of forms. 



(Key to species and varieties}. 



a. Parietal tooth minute, not connected with columellar lip by a 

 raised callus ; no internal lamina. paludosa. 



aa. Parietal tooth connected with a raised parietal callus. 



b. Internal lamina present; upper surface strongly ribbed. 

 c. Size large ; whorls 7-10. cereolus. 



