1904.] NATURAL SCIENCES OF PHILADELPHIA. 413 



tions. How many other species still survived in the less altered sec- 

 tions it is impossible to say. It is hardly possible to prove that even 

 the set of fossils from No. 806 belong to any earlier date. Indeed we 

 might draw an analogy between Bifidaria rupicola at No. 806, which 

 may be one of the later arrivals, and Bifidaria servilis at No. 818 and 

 Piipoides marginatus at No. 809, either of which we can hardly hesitate 

 to treat as recent arrivals. But however this may be, the sand-pit 

 deposits are against the supposition that the Carychiwn and its hardier 

 associates were exterminated merely by the increasing barrenness of 

 the island. We should be in a better position to discuss the other 

 causes if we knew whether these species survived till after the West 

 Indian arrivals had begun to take possession of the land. The West 

 Indies snails, especially Polygyra microdonta, of Bahama, are at present 

 much the commonest of the ''native" snails, and it may be that their 

 special fitness for the more barren land of the new Bermuda made them 

 deadly competitors to the old species. The newer formations at the 

 west end of the islands, which I had not the time to visit, may perhaps 

 be the ones in which to look for evidence on this question. 



Notes and Descriptions. 



Thysanophora vortex Pfr. 



Living animals quite abundant under stones; but I looked in ^•ain 

 for fossil specimens. Greater Antilles, Bahamas, Southern Florida. 

 Thysanophora hypolepta ' Shuttl.' Pils. 



I foimd more examples of this than of Z. 77iinusculus among the 

 fossils, but among the living snails Z. minusculus seems to be far more 

 abundant. It is supposed to be indigenous. 

 Polygyra microdonta Desh. 



Excluding importations from Europe, this species is the one now most 

 in evidence. It is partial to the coarse native grass, but is to be found 

 almost everywhere. I was surprised not to find any indubitable 

 specimens of this in the sand pits. I hope other collectors will look 

 for it. Bahamas. 

 Strobilops hubbardi Brown. 



An adult and an immature specimen, from locality 806. The adult 

 is somewhat larger than the usual size on, the continent. Alt. 1.2, 

 diam. 2.8 mm. Habitat, ther Gulf States and Jamaica. 



Vertigo numellata n. sp. PI. XXXVI, fig 6. 



Shell rimate, minute, elliptical or bluntly pupiform, yellowish- 

 corneous, faintly striate, of 5 rather convex whorls; the diameter 

 through the body whorl not much greater than that through the whorl 



