1910.] 



NATURAL SCIENCES OF PHILADELPHIA. 



95 



elevations than the Rucker Box (about 7,000 feet), so that the degen- 

 eration is probably due to other local causes. 



Ow 



Fig. 15. — O. b. minima P. and F., Rucker Canyon, Station llha. 

 Genus ASHMUNELLA Pils. and Ckll. 



A study of the genitalia of Chiricahuan Ashmunellas leads to the 

 conclusion that all the species of that range are of common ancestry, 

 and more closely related inter se than any are to New Mexican or 

 Huachucan species. In other words, the specific differentiation has 

 been mainly subsequent to the isolation of this fauna. 



In both Chiricahuan and Huachucan species the penis is bipartite, 

 consisting of an upper and a lower portion separated by a submedian 

 constriction. In the Huachucan 

 series the upper segment is enlarged 

 like the lower (see plate XX, Proc. 

 A. N. 8. Phila., 1909). In 



Chiricahuan forms the upper seg- 

 ment of the penis is very narroiv, 

 hardly larger than the epiph alius, 

 but its distal end is invariably a 

 little swollen, and contracts 

 abruptly where it passes into the 

 epiphallus 20 . The penis retractor 

 is extremely short in Chiricahuan 

 species, longer in Huachucan. 

 The spermatheca is more or less 

 varicose in Huachucan species, 



but this is hardly apparent in Chiricahuan forms. The vagina in the 

 Chiricahuan series is swollen and muscular in its upper part, smaller 

 with thinner walls below. In other respects the organs are alike in 

 the two series. These considerations lead to the conclusion that the 

 whole Chiricahuan series of Ashmunella constitutes one phylum, the 

 Huachucan series another. Doubtless the two phyla were of common 

 ancestry; but their evolution on the two parallel mountain ranges 

 has been independent. The extraordinary resemblances between 

 some Chiricahuan and Huachucan species, which led us in 1905 to 



20 The slender upper continuation of the penis was not always recognized in 

 our former (1905; work on Chiricahuan snails, although once understood it is 

 clear enough. 



Fig. 16. — Terminal ducts of genitalia 

 of Ashmunella p.albicauda, Station 4, 

 White Tail Canyon. Sp, base of 

 spermathecal duct; Ori, base of ovi- 

 duct; P, lower, swollen portion of 

 penis; p, upper end of penis. 



