572 PROCEEDINGS OF THE ACADEMY OF [AufrilSt, 



Lanai. Dr. W. Newcomb collection, Cornell University Museum. 



The specimens here described and figured are from Newcomb's 

 collection, and since Pfeiffer's types were from Newcomb, it maybe in- 

 ferred that they were from the same lot. In view of Dr. Pfeiffer's well- 

 known accuracy as a diagnostician, it is hard to believe that his descrip- 

 tion of Helix alata was based upon the same species, since it disagrees 

 in the number of whorls and shape of the spire, and in omitting a refer- 

 ence to the columellar lamella. It is possible that two species were 

 present in Newcomb's collection, and what Pfeiffer actually described 

 was a Pterodiscus close to P. ivesleyi. This could be decided by a 

 reference to Pfeiffer's own collection. Mr. Sykes, who had occasion to 

 correct the senior author's former identification of H. alaUi, did not 

 take the trouble to place the species upon a recognizable basis. 



Genus PTERODISCUS Pilsbry. 

 Manual of Conchology (Series 2), IX p. 36, November 16, 1803. 



Shell openly umbilicate, discoidal or subdiscoidal, thin, uniform 

 brown, and carinatc at the periphery. Peristome simple or expanded, 

 the columellar lip dilated. Axis and columella smooth, without a 

 spiral lamella. Jaw and radula as in Amastra. Type P. tceslcyi Sykes 

 { = Endodonla alata Pils., not Helix alata Pfr.?). This group was origi- 

 nally established as a section of Endodonta. Mr. Sykes elevated it^ to a 

 genus of the Endodontidcs . The examination of the jaw and radula of 

 P. digonophora shows it to belong to the Achatinellidce; and in that 

 group it stands close to Helicamastra, from which it is differentiated 

 solely l)y the total loss of the columellar lamella. In shape, texture, 

 sculpture and the structure of the early whorls, Pterodiscus and Helica- 

 mastra agree very closely. 



The jaw of P. digonophora is very thin, deeply arcuate, smooth except 

 for a few wide plaits or flat ribs in the median part. 



.XlV 



The radula of P. digonophora has 11, 7, 1, 7, 11 teeth. Those of the 

 median field stand in nearly straight transverse rows, but at the sides 

 the rows of marginal teeth bend rapidly forward. The centrals are 

 narrow, less than half the width of the adjacent lateral teeth, and bear 

 a single small cusp. The lateral teeth are square, bicuspid with a large 



