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. (Sée 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 
