TIE WEST INDIAN FAUNA. uni 
secondary, or tertiary times. This extension of geographical 
range in the case of so many of the species of the Caribbean 
fauna is most instructive. As has been observed in several 
groups of invertebrates, and in fishes, the presence of identi- 
cal species on the two sides of the Isthmus of Panama points 
to a comparatively recent communication between the Atlantic 
and Pacific, while the presence of cosmopolitan species at such 
distant points as the Caribbean, Australia, and the Red Sea in- 
dicates a connection which could have been effected only by 
migration on the floor of the ocean or in the track of currents. 
The sponges apparently have a wide geographical distribu- 
tion, many of them being cosmopolitan. A number of mol- 
lusks also have au extraordinary geographical range, from 
Northern Europe to the Cape of Good Hope or to Patagonia. 
Others are found in the seas of Great Britain, at the Cape of 
Good Hope, and in the Southern Ocean. Others again are 
denizens of the arctic and antaretie seas, or extend from the 
northern parts of the Pacific to the Kerguelen Islands. 
A number of species of deep-sea corals and gorgonians ex- 
tend northward in deep water from the Caribbean district along 
the east coast of the United States. A few species of simple 
corals like Flabellum and Fungia have a great geographical and 
bathymetrical range. Half a dozen species of corals are com- 
mon to the northern seas of Europe and the Straits of Florida. 
From the geographical distribution of the corals, and their affin- 
ity with the tertiary fossils of Italy, Pourtalés came to the con- 
clusion that the tertiary deep-sea fauna of Europe has as it were 
migrated westward and maintained itself, while the greater part 
of the contemporaneous forms of the West Indian deep sea 
have become extinct. 
The collections obtained by the * Blake" in the Caribbean 
district are superior, as regards the number of duplicates, to 
those made by the * Challenger." Many species occur, not only 
in large numbers, but also at several localities ; so that it has 
been possible to study their range of variation in a more satis- 
factory manner than hitherto. This opportunity has proved of 
immense value in revealing the existence of many intermediate 
forms between types which were considered quite distinet. 
