396 7'. Bland on the Geographical Distribution of Mollusca. 
California, nearly in 28° N. Jat.; but none of them inhabit San 
Diego, which is near 33° N. lat. In the same manner the south- 
ern limit is found near the boundary between Peru and Chili, 
between 22° and 24° S. lat. 
The reason why the range of the species south of the equator 
is several degrees less than on the north side, is obvious in the 
Antarctic current, which sets along the west coast of South Amer- 
ica. In like manner, on the eastern coast of North America, a 
polar current appears to extend the Arctic Fauna of marine shells 
to 41°. lat., and the cold current along the shores of the Middle 
and Southern States seems to limit the tropical Fauna to about 
26° or 28° N. lat. on the coast, although on the east side of the 
Gulf Stream it extends to the Bermuda Islands in latitude 32° N. 
It will also be seen in the following pages, that a large number 
of the species which occur at Panama were collected by Mr. 
Cuming at the Gallapago Islands. But if any of the species oc- 
cur in the Polynesian Islands, the number does not exceed three 
or four, and in these cases the specific identity of the shells is very 
doubtful. The western boundary of the Panama province may 
therefore be made to include only the Gallapago Islands.”—p. 5. 
Professor Adams gives a list of 20 species collected by him at 
Panama and T'aboga, which occur algo at the Gallapago Islands, 
from which it appears, that a larger Moan of the littoral than 
of the pelagic known species are common to the Gallapago Islands, 
and the main land; and of the pelagic species, all which are 
known inhabit moderate depths. 
With regard to the limits of the Caribbean province, Professor 
Adams remarks that very few of the Caribbean species “ occur 
north of the Bahamas, or south of Brazil, although from various 
sources of error many of them have been reputed to inhabit Eng- 
land, and various other parts of the world. Although there are 
several analogous species in the two provinces, in general there 
is a great dissimilarity.” 
The author thus concludes his Introduction :— : 
“A great amount of valuable materials, for interesting generali- 
zations on the number and distribution of the species of marine 
Mollusks, has been collected by public and private expeditions. 
But when we consider the immense profusion of species and o 
individuals in tropical seas, and the confusion of the habitats of | 
‘ner which would justly inspire cont 
