CATALOGUE OF MARINE SHELLS, COLLECTED 

 CHIEFLY ON THE EASTERN SHORE OF LOWER 

 CALIFORNIA FOR THE CALIFORNIA ACADEMY 

 OF SCIENCES DURING 1891-2. 



The Gulf of California is the richest field for molluscan 

 collections outside of the tropics along the whole west 

 American coast, principally for the reason that, being 

 nearly landlocked and opening only southward, it is al- 

 most as tropical as the more southern waters toward' the 

 Equator, and perhaps even warmer than some regions 

 where currents from the north have free circulation. 

 The contrast is thus strongly shown between the gulf and 

 the western coast of the peninsula, in the small proportion 

 of tropical species found on the latter and their more lim- 

 ited range northward. 



The length of the gulf is about 760 miles northward of 

 the latitude of Cape St. Lucas (22" 52'), and of this only 

 forty-four miles are south of the Tropic of Cancer, while 

 the width averages about fifty miles. The influx of the 

 Colorado and other smaller rivers serves to keep the wa- 

 ter from becoming too salt for molluscan life, and, though 

 evaporation must be enormous, it seems thus balanced, 

 while the usual differences in the species found in brack- 

 ish waters are observed to only a limited extent compared 

 with gulfs of less depth, like the Gulf of Mexico. Still, 

 there are many species identical in both gulfs, and many 

 analogies with the species found in the Mediterranean 

 and Red seas, which are the most similar waters of the 

 eastern continent. 



Some of the most important collections from the gulf 

 previously made are mentioned in Carpenter's "Mollusks 

 of Western North America," Smithsonian Edition, 1872, 

 and will give some idea of the number of species found 

 there. The first well recorded were collected in 1825, 



2d Ser., Vol. V. May 21, 1895. 



