1905.] NATURAL SCIENCES OF PHILADELPHIA. 269 



The penis is well developed, its lower part being muscular, and pli- 

 cate within, the upper part thinner and densely, finely papillose inside. 

 The epiphallus is well developed, with terminal vas deferens or with a 

 terminal tubercle (representing the flagellum) and a sublaterally in- 

 serted vas deferens. The vagina is rather long. The globular or ovate 

 spermatheca terminates a slender duct nearly as long as the uterus. 

 Reproduction is viviparous. 



The retractor muscle of the penis arises from the apex of the penis 

 and base of the epiphallus, or from the epiphallus near its base, and is 

 inserted on the lung floor. The right ocular retractor passes between 

 the (2^ and 9 branches of the genitalia. 



The jaw is strong, arcuate, its anterior face more or less distinctly 

 striated vertically; and there are sometimes very weak traces of ribs. 

 The radula is of the ordinary Helicid type. In some species the median 

 area has unicuspid teeth, the cutting-edges usually overhanging the 

 sides of the mesocone; while in others distinct ectocones are developed 

 in all the teeth. The marginal teeth are bicuspid, the cusps unsplit 

 as a rule, though there are exceptions where the inner of the two cusps 

 is bifid. 



Type Helix strigosa Gld. Distribution, Rocky ^Mountain region from 

 the Canadian to the Mexican boundary. 



This dominant type of Helicidce in the area indicated above formerly 

 extended farther east, one species occurring in the loess of Iowa, and 

 there is one outlying species westward, 0. avalonensis Hemph., on 

 Catalina Island, California. In its present area the type has been in- 

 terminably modified into local races of all grades of differentiation, 

 more than fifty of these having received names.^ It is true that in some 

 ranges every canyon— I might almost say every rock-heap — has its own 

 race ; but in a broader view it is seen that a single strain usualh' extends 

 over an entire range with numerous minor modifications, and with 

 increasing elevation a general diminution of size, loss of sculpture and 

 often intensification of color. These reduced forms are probably due 

 to the diminished food supply and especially the shorter growing season 

 in the heights — factors subject to great local variation, even at equal 



' The number of species of Oreohelix is uncertain. About fifty forms of all 

 degrees of differentiation have been described and named. My treatment of the 

 group in former pubhcations (Manual of Conchology, VIII, p. 11.5, IX, p. 50; 

 Catalogue of the Land Sheli'^ of America, etc., pp. 31, 32 (1898), was unchily influ- 

 enced by iihe views of Binnej' and Hemphill, both of whom advocated the inclusion 

 of the entire series as varieties of P. strigosa. The cliaracters of the shells, 

 penes and teeth indicate, in my opinion, that the species are somewhat' numer- 

 ous; but their notorious variability cautions us to beware of multiplying tliem 

 without ample materials. 



