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 
Pupoides 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 Carychium 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 vain 
for fossil specimens. Greater Antilles, Bahamas, Southern Florida. 
Thysanophora hypolepta ‘Shuttl.’ Pils. 
I found more examples of this than of Z. minusculus 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. 2.8mm. Habitat, the Gulf States and Jamaica. 
Vertigo numellata n.sp. Pl. 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 
