288 FROCEEDINGS OF THE ACADEMY OF [1888. 



And since the island is typically oceanic, "a solitary peak rising 

 abruptly from a base only 120 miles in diameter" surrounded on all 

 sides by between 2500 and oOOO fathoms depth, we have an indica- 

 tion here that land raollusks of many families, Helicidce, Zonitidce, 

 Siieeliiidw, FupidiE, Hclicinida:, even Vagiiiu/uke, (for a large uudes- 

 cribed species of Vaghmlas exists upon the island) may be trans- 

 ported very great distances by sea, by, in all i)robability, the agencies 

 mentioned above. 



The considerable divergence existing between the vai'ious species 

 of the Zonitoid genus peculiar to Bermuda, Poecilozoiiites, indicates 

 that the island is of considerable antitiuitv. 



AVe may define the genus as follows : 



POECILOZONITES. 



Generic characters : Shell helicoid, subtrochiform, depressed conic, 

 or subdiscoidal, perforate or umbilicate, obliquely striate, ornament- 

 ed with radiating zigzag flammules or spiral bauds of chestnut color 

 on a lighter ground ; whorls numerous (7-10) very slowly widening ; 

 body whorl more or less flattened or compressed below the usually 

 cariuate periphery, not descending anteriorly ; aperture more or 

 less irregularly lunate ; peristome simple, the columellar margin 

 slightly ex})an(led and thickened with a white callus which encircles 

 the pillar within. Animal similar in form to Helix; foot narrow, 

 short posteriorly, scarcely reaching behind the shell, without longi- 

 tudinal furrows above its margin or caudal nuicous pore; orifice of 

 genitalia on the right side of neck, near, but not under tlic mantle; 

 mantle margin simple; jaw like t)iat of Limax, very thin, arcuate, 

 with a broad Iilunt median projection anteriorly ; radula with 

 tricuspid central teeth having quadrate basal plates, the central 

 cusps })rqiecting beyond the anterior margins of the basal plates, the 

 side cusps rather short, with well reflexed cutting points ; lateral 

 teeth similar but asymmetrical, lacking the inner cusps ; marginal 

 teeth aculeate, with simple thorn-shaped cusps and oval basal plates. 

 It will be seen by the above definition that the genus cannot be 

 included in any of the groups with which its species have been 

 associated by authors ; the Zonitoid dentition at once removing it 

 from the Helicidce, and the absence of a caudal mucous pore, the 

 more anterior position of the orifice of the genitalia and the coloration 

 • of the shell, separating it from Zonites and its subgenera. 



