LOWER CALIFORNIAN MOLLUSCA. 213 



closely resembling a large B . piln/a from Point Arena, 

 but the full-grown are thickened more than any of either 

 form, the mouth of two having a heavy callous connect- 

 ing the lips, and in one developing a blunt tooth on the 

 inner wall. (This excessive thickening is also found in 

 a var. of Helix arcolata from the same island.) The 

 umbilicus is like that of B. sufflatns of same size, and 

 also as in large B.pilithi. It is 1.20 inch long, 0.70 wide, 

 mouth 0.65 long, 0.50 wide, in most thickened specimens ; 

 no distinct expansion of lip, but its margin is thickened. 

 All these forms, which appear to be subspecies of one 

 original species, have 5^ whorls, but specimens of the 

 size of Binney's figure have but five (or even four, as he 

 gives it, which is probably a proof of immaturity). 



B. XANTUsi W.G. Binney, 1861. Of this Xantus only 

 got four on the promontory. Mr. Bryant found 12 at the 

 Rancho Lagunas, near Point Arena, not much above the 

 level of the gulf. Mr. Eisen found 116 on the Sierra 

 Laguna, mostly near La Chuparosa, 2,000 feet altitude, 

 and all were dead, only 22 retaining any of the brown 

 epidermis of living shells. The punctures given by Bin- 

 ney as the sculpture, are caused by erosion or imperfec- 

 tion of the shell, as they are entirely beneath the epider- 

 mis. The most perfect shell has narrow lines of dark 

 and light brown alternating, as in B .altcrnatus, and some 

 show these stripes in the shell also. The form varies 

 from a short to a long oval, measuring 0.70 inch long and 

 0.50 wide to 0.85 long and O.45 wide, which is the size of 

 Binney's figure. I cannot detect an}^ "minute revolving- 

 lines" on these specimens, and the ''wavy stria^ " are 

 only on broken lines of growth. Adults have the outer 

 lip slightly everted, and in one the vertical riblets usual 

 to the group can be seen faintly in the epidermis of the 

 two nuclear whorls (worn off in the others). 



