NATURAL SCIENCES OF PHILADELPHIA. 285 



May 1, 1873. 



Meeting of the Conchological Section. 

 Dr. RuscHENBERQER, Director, in the chair. 



Mr. Tryon called attention to an interesting series of land and 

 fluviatile Mollusca from Utah, presented this evening. 



These shells were collected by the Wheeler Exploring Expedi- 

 tion, acting under authority of the U. S. Engineer Office at 

 Washington. 



The specimens of Helix .ntrigosa, Gould, exhibit every variation 

 of form from the typical shells with depressed rounded whorls 

 and smooth surface, to those with several revolving raised lines 

 and a carinated periphery ; in the latter condition they are iden- 

 tical with H. Heniphillii, Newcomb (Amer. Journ. Conch, v. 165, 

 1869, "White Pine Mining District"). In others, again, the 

 raised lines are more numerous and sufficiently prominent to be 

 called ribs, and the periphery is not carinated ; in this state they 

 are H. Raydeni, Gabb (Am. Journ. Conch, v. 24, 1869). 



The latter species has been heretofore considered to belong to 

 a new generic type for America, being the onh' species having 

 revolving ribs : its nearest relationship was apparently with a 

 small group of Madeiran Helices. The form of the shell, its 

 external appearance, and the closely approaching extremities of 

 the labrum, connected by a callus upon the parietal wall, reminds 

 one of Gyclostoma ; but no opercula were obtained with the fifty 

 odd specimens in semi-fossilized condition, collected by Prof. F. 

 V. Haj'den, in Webber Canon, Utah. 



It is extraordinary that any species should be found to vary so 

 much as does H. sti'igosa, in those characters which have hei'eto- 

 fore been regarded as most persistent and distinctive. It is much 

 easier to imagine the growth lines developed into ribs, than a 

 form in which the gi'owth lines are crossed by revolving ribs. In 

 H. Idahoensis, Newcomb (Ibid. ii. 1, 1866), we find the surface 

 raised into sharp i-ibs parallel with the lines of accretion, and, as 

 in all other respects, this species does not appear to differ from 

 strigosa; it is very probable that Idahoensis will also prove to be 

 a variety of this protean species. 



