DIMYARIA UNIONIDAE ANODONTA DEJECTA. 953 



that of an arcuate Man/ar/tana mar</inata. The lines of growth indicating 

 the form of the half-grown shell betray its resemblance to a very transverse 

 inflated Unio tappaniamis. There is no familiar species of Anodonta with 

 which this species is comparable." 



The following has been furnished me by Mr. Tryon for incorporation 

 in this report : 



" Extract from a verbal communication made by Mr. G. W. Tryon, jr., of the 



Academy of Natural Sciences of Philadelphia, to the Conchological Section 



of the Academy, May, 1873. 



" Mr. Tryon called attention to an interesting 1 series of land and fluviatile 

 Mollusca from Utah, presented this evening. These shells were collected 

 by the Expedition for explorations west of the one-hundredth meridian, 

 acting under the authority of the United States Engineer Office at Wash- 

 ington. 



"The specimens of Helix strigosa, Gould, exhibited 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 peri- 

 phery ; in the latter condition, they are identical with H. hemphiUii, New- 

 comb (Am. Jour, of Conch., v, 18G9, 165, 'White Pine Mining District'). 

 In others, again, the raised lines are more numerous, and sufficiently promi- 

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

 are H. haydeni, Gabb (Am. Jour. Conch., v, 1869, 24). This little species 

 has been heretofore considered to belong to a new generic type for America, 

 being the only species having revolving ribs ; its nearest relationship was 

 apparently with a small group of Madeira Helices. The form of the shell, 

 its external appearance, and the closely approaching extremities of the lab- 

 rum, connected by a callus upon the parietal wall, reminds one of Cyclo- 

 stoma ; but no opercula were obtained with the fifty odd specimens in semi- 

 fossilized condition collected by Prof. F. V. Hayden, in Weber Canon, 

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

 much as does H. strigosa in those characters which have heretofore 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 growth lines 



