LOWER CALIFORNIAN MOLLUSCA. 217 



LiMAx. There is a species from the mountains which 

 has not yet been identified. 



LiMNOPHYSA HUMiLis Say, 1822. Also common in the 

 ponds of Sierra Laguna, at some height. Before known 

 as far south as latitude 31^ 51'. 



Physa gabbi Tryon. Specimens from high on the 

 mountains, where it is very abundant in streams. 



Planorbis tumens Carpenter, 1857, and var. occi- 

 DENTALis J. G. C, 1870. Many specimens from a dry 

 pond at San Jose del Cabo, sent by Eisen, prove the oc- 

 currence of this species nearly opposite Mazatlan, from 

 whence it was first described, and also that it there attains 

 the large size and five whorls described by me as found 

 northward. The only difference from California speci- 

 mens seen in them is their narrowness, which aids them 

 in crawling through the dense water vegetation, and is, no 

 doubt, a local variation caused by the density of aquatic 

 vegetation in a tropical climate. 



Planorbis subcrenatus Carpenter. A number of 

 this species, brought by Mr. Bryant from some part of 

 the west coast of the peninsula, prove on comparison to 

 represent the other large west coast species. Their chief 

 difference is seen in specimens of each of the same size 

 showing one less whorl above in this, which also has the 

 whorls rounder and the sculpture stronger. 



Three other small species of this family, two differing 

 subgenerically from any in the United States, remain to 

 be worked up. 



PisiDiuM (abditum) occidentale Newcomb. The 

 only fresh-water bivalve from the peninsula, was found 

 of all sizes, rather common in ponds on the Sierra 

 Laguna, but showing no differences from the common 

 shell northward. 



