254 PROCEEDINGS OF THE ACADEMY OF ' [Mch., 



size and minor details of shape and sculpture, show with few exceptions 

 no prominent specific differentiation. On the other hand, in the inter- 

 nal anatomy there has been a good deal of divergence. A few forms, 

 such as S. lohrii Gabb and S. wolcottiana Bartsch, seem to be quite dis- 

 tinct conchologically, but in many cases the determination of speci- 

 mens of the shells other than the type localities is so uncertain as to 

 be little better than guesswork, even when types are available for 

 comparison. In dealing with these ambiguous forms I have thought 

 the interests of science best furthered by applying specific names only 

 to those I am able to characterize anatomically, and thus put upon a 

 secure basis. 



An illustrated monograph of Sonorella, dealing with the shells 

 only, has been 'published by Mr. Paul Bartsch, who has devoted 

 great industry to the elucidation of the numerous species and 

 races. The work is of permanent value for its exact descriptions and 

 excellent figures, both of which I have had occasion to test; but it 

 deals with selected or "type" specimens only, ignoring the fact of 

 variation, and hence fails to give a just idea of the complex of varying 

 forms which exist, or even of the variations of size, etc., occurring in 

 the type lots. I would here express my indebtedness to Mr. Bartsch 

 for his invariable kindness in comparing for me various forms of *S. 

 hachitana with specimens in the U. S. National Museum. 



Mr. Bartsch has made the valuable observation that the embryonic 

 shells of Sonorella are sculptured, usually with oblique forwardly de- 

 scending threads, or with two sets of intersecting threads, sometimes 

 interrupted to form papilloe at their intersections. This sculptiu-e may, 

 I think, be the accelerated vestige of a somewhat similar sculpture 

 characteristic of the Californian Helices in their adult stage, and 

 which may thus have been common to the ancestral SonorcUas. 



The relationships of Sonorella are primarily with Oreohelix and Ash- 

 viunella. It differs from Oreohelix chiefly in the different proportions 

 of the kidney and pericardium, but also in the structure of the shell, 

 the oviparous reproduction, the unkeeled young shell, and in the dis- 

 tinctly ribbed jaw. 



Sonorella stands nearer Ashmunella in internal anatomy, but there 

 is a constant difference in the male organs, the penis being well devel- 

 oped in Sonorella, while in Ashmunella it is more or less completely 

 degenerate, the epiphallus being hypertrophic. The divergence between 

 the shells of the two genera is conspicuous. So far as the shell is con- 

 cerned, Sonorella stands nearer to the generally prevalent type of 

 Belogonous Helices than do either of the other genera. 



