1909.] NATURAL SCIENCES OF PHILADELPHIA. 499 



In one specimen dissected it bears a minute diverticulum about 1 mm. 

 long, 2 mm. from the base of the duct. In another individual no 

 diverticulum was found, so that it may possibly be abnormal or 

 pathologic. The measurements of the organs in two individuals 

 preserved in formalin follow: 



No. 94,384. No. 94,358. 



Length of penis, 39 mm. 41 mm. 



" penis-papilla, 8 " 9 



" epiphallus, ....... 49 " 60 



" flagellum, 4 " 3 



" " vagina, 25 



" " spermatheca and duct, .... 34 " 27 



The jaw (pi. XXII, fig. 6) has five strong ribs grouped in the middle 

 half of its length. 



The radula has about 41, 1, 41 teeth (pi. XXII, fig. 8). The central 

 and lateral teeth have mesocones only; on the 17th an ectocone appears. 

 On the outer marginal teeth the inner cusp or sometimes both cusps are 

 bifid, but the ectocone is not split into several cusps as in some other 

 species. 



The excessive length of penis and epiphallus, and especially the 

 hollow, thin-walled papilla containing a separate duct or tube (a 

 structure unique in the genus), are characters which set S. dalli apart 

 from all other known Sonorellas. It stands alone in its own line of 

 differentiation. 



Group of S. granulatissima. 



These forms are closely related to the group of S. hachitana, but 

 differ by the thick, quite cylindric penis-papilla, solid except for the 

 minute perforation, and very obtuse or truncate at its distal end, 

 and by having no flagellum or only a minute vestigeal one. In the 

 hachitana group the papilla tapers, at least at the distal end, and a 

 minute but distinctly developed flagellum is present in known forms. 

 The distinction is only a small matter, but serves to distinguish the 

 Huachucan forms. S. rowelli (Newc), from a little farther west, 

 belongs to the same group. 



The dimensions of the genitalia in several specimens of each form 

 are given in the accompanying table. Most of the specimens were 

 preserved in alcohol in the field, and some variation is doubtless 

 traceable to various degrees of contraction. 



