The Nautilus. 



Vol, XXIX. AUGUST, 1915. No. 4 



APICAL CHARACTEES IN SOMATOGYEUS, WITH DESCEIPTIOFS 

 OF THREE NEW SPECIES. 



BY BRYANT WALKER 



In his description of Somatogyrus walkerianus^ (Naut., xviii, 

 p. 140), Aldrich stated that ' ' the nucleus is obliquely placed 

 and projects markedly beyond the outline of the spire on the 

 left side." This is the only observation that has been pub- 

 lished with reference to any special apical characters in this 

 genus. 



Recently, while studying several lots of Somatogyrus collected 

 by Messrs. Hinkley and Wheeler in Arkansas, I noticed, while 

 examining an uneroded specimen with an ordinary glass, that 

 not only was the apical whorl decidedly everted, but that it was 

 apparently punctate. On putting it under a compound lens 

 the spirally punctate sculpture was clearly developed. This 

 led to a careful study of all of the described species with some 

 very interesting results. 



The irregular coiling of the apical whorl, or partial aversion, 

 as it were, is very common in Somatogyrus and is found, to a 

 greater or less extent in all of the species in which the spire is 

 more or less conically elevated and acute. In species having 

 the apical whorls flattened, of which S. strengii is a conspicuous 

 example, no eversion is found. 



The amount of apical eversion varies not only in the different 

 species, but also in individuals of the same species. But wlien 



