LOWER CALIFORNIAN MOLLUSCA. . 1 35 



this last collection a form connecting still more closely 

 the B . vegetus with B . montczuina, which may be called 

 either a white variety of the last or a rough variety of the 

 first, the sculpture being as strongly shown. I have had 

 this lithographed from a photograph, enlarged 15 diame- 

 ters. The present forms, now called species, were prob- 

 ably much more closely connected when this region was 

 an island. 



C. Section Leptobyrsus Crosse & Fischer. 



These authors are followed by Dall in making this 

 division of Buliniulus to include some species resembling 

 B. spirifcr Gabb, in having a more strongly twisted pil- 

 lar in the upper part of the body-whorl, as in pi. v, fig. 4. 

 Sometimes this has also a lamina more or less widely de- 

 veloped, which is continued to the mouth '' as a fold or 

 rounded ridge such as appears in the various species of 

 subsection A." Now, under B. sufflatus Gould, Dall 

 says: " In specimens which have survived a dry season 

 attached to bark or stone the inside of the peristome and 

 the space on the body between the two lips is often much 

 thickened by a deposit of callus." I have also recorded 

 this thickening and abnormal development of teeth in 

 some island species, but attribute it to food and other 

 causes. 



I am of the opinion that the growth of the wide lamina 

 in some specimens is also an abnormal deposit, and caused, 

 perhaps, by irritation of the muscles used in holding up 

 the shell when attached to a vertical surface of rock or 

 tree. Even the extra twist of the pillar is explainable on 

 the same principle like the divergent mouth, none of these 

 characters being constant. I give a view of a shell with 

 this pillar twist that in everything else is a B . inscendcns, 

 yet Dall would make it a ^'■B. bryanti,'" according to his 

 theory, on account of an abnormal and perhaps a patho- 



