1916.] 



NATURAL SCIENCES OF PHILADELPHIA. 



349 



This is the form which was at one time identified as 0. haydeni 

 gabbiana. It resembles 0. h. hybrida very closely, but the embryonic 

 stage differs. The last embryonic whorl is not so convex in mixta, 

 and its major spirals are more distinct and the radial ripples are 

 more irregular. The carina is decidedly more prominent, and the 

 whorl as a whole is distinctly more depressed. It is likely that 

 hybrida and mixta are independent forms of the haydeni stock, or 

 perhaps separated relics of a pro-haydeni race. 



Some specimens have much the appearance of cooperi, but the 

 genitalia show that there is no real connection. There is large 

 individual variation in the height of the spire. 



The embryonic shell of 0. h. gabbiana has stronger spirals both 

 above and below near the end of the last embryonic whorl; its 

 periphery is less pinched out, and it is less depressed. The adult 

 gabbiana is usually more strongly angular or keeled. 

 Oreohelix peripherica (Ancey). PI. 20, figs, l to 6. 



In genitalia this species does not differ materially from 0. strigosa 

 depressa (b) and 0. haydeni. The internally costate part of the penis 

 is less than half of the total length, usually slightly over a third. 

 The internally papillose distal portion usually collapses flat, but one 

 specimen from Station 30 and one from 36 there are weak indica- 

 tions of a third ridge. The cylindric lower part of the penis has 

 5 or 6 longitudinal ribs within. 



Many specimens were opened, from various localities, and including 

 nearly smooth, fine-ribbed and coarse-ribbed, white and banded 

 individuals. Except in size, there is very little variation. 



Measurements, in mm., of the genitalia of Oreohelix peripherica. 



