24 Lower Californian Shells. [zoe 



is a barren saline plain. The mountains west of it are less barren, 

 and must contain some of the species reported from the region 

 westward, near the ocean. No. 20 probably exists there also, as it 

 extends into California, Arizona, and on the peninsula. (See notes 

 on it.) 



In reviewing this catalogue we find the terrestrial species to be 

 thirty-two, of which fourteen are found on both sides of the bound- 

 ary line. The fresh-water species are but eleven (or twelve count- 

 ing No. 37), and all but this and perhaps 36 cross the boundary. 

 Thus there remain, not found northward, eighteen land species* 

 and one or two fresh-water. 



Those also found on the east side of the gulf, or further south, 

 are four or five land and four fresh- water. The total number given, 

 including marine, is fifty-three, of which fourteen are considered 

 peculiar to the peninsula, and two are reported as Chilian also (in- 

 cluded in those more southern). Of the peculiar forms eight are 

 Bulimoid, and four Helicoid. The derivation of these, peculiar to 

 the peninsula, will in future be an interesting subject for investiga- 

 tion. 



In referring to Lower California as "the Peninsula" it is most 

 correct to include in it only the regions south of the mouth of the 

 Colorado River, about lat. 31° 30', which excludes the Desert spe- 

 cies and also Nos. 15, 18, 24, 25, 26, 27, as their range is now 

 known. 



The local distribution of the species depends on latitude, altitude 

 and exposure to the gulf on the east, or the ocean on the west. The 

 gulf having heated water and tropical marine mollusca, besides 

 having its shore protected from the ocean winds by high mountains, 

 shows the greatest number of tropical species on land, the same 

 species sometimes extending four or five degrees of latitude farther 

 north than on the west coast. It is doubtful if any but Helicoid 

 species are found on the west coast north of lat, 25°, while those of 

 the east coast are mostly Bulimoid. Nos. 20 and 23 are the most 

 southern of the former on east side, at lat. 26° 52', about 280 miles 

 north of Cape St. Lucas. Very much yet remains to be learned 

 regarding distribution of the species. 



The most remarkable instance of peculiar distribution is that of 

 the three or four species inhabiting Guadelupe Island, on which we 

 might expect a much larger number to occur, judging from most 



