MOLLUSCA OF PORTO RICO. 
355 
marine fauna of the region of which it forms a part. The extraordinary richness of 
some spots, as in Mayaguez Harbor, where a few hauls of the dredge were taken, 
affords sufficient evidence that there is no unusual paucity of molluscan life about the 
island in proper situations. Hence we may reasonably expect the total census of 
shell-bearing mollusks, when carefully made, not to fall short of the average above 
indicated for such faunas. Excluding land and fresh-water shells, and nudibranchs, 
the total number of species and well-marked varieties included in the present report 
is 530. We may therefore suspect that about 70 marine species, actually existing 
somewhere about the island, remain to be collected and identified before our catalogue 
can be regarded as approximately complete. 
The most interesting feature of what we may call the West Indian fauna as a 
whole is its extent beyond the limits which have been ordinarily assigned to it. Off 
the eastern coast of North America, outside of the narrow strip of colder water which 
makes its way close inshore nearly to the coast of Georgia, the West Indian fauna 
in the warm waters of the Gulf and equatorial currents extends northward over the 
vast area of the continental plateau and slope fully to the latitude of Cape Hatteras, 
as has been proved by the dredgings of the U. S. Fish Commission. On the south 
the species extend along the coast of Brazil to the estuary of the River La Plata, 
though in constantly diminishing numbers. 
As on the Pacific shore the Panamic fauna stretches from Point Conception, Cal., 
south to the Bay of Guayaquil, so the companion fauna of the West Indies covers an 
even greater extent of coast, on which it may doubtless hereafter be divided into 
a certain number of subordinate faunulse. The fact that the stretch of coast now 
sterilized by the fresh waters of the Amazonas has not acted as a barrier is tolerably 
good evidence that the existing distribution, in its main features, antedates the 
formation of this immense river system. 
The number of new species among the marine forms collected by the U. S. Fish 
Commission and described in this report is 42. The total number of species accounted 
for in the present report may be tabulated as follows: 
Cephalopoda 
Pteropoda 
Gastropoda: 
Tectibranehiata 
Nudibranchiata 
Pulmonata: 
Akteophila 
Ditremata 
Limnophila 
Geophila 
Orthodonta, marine . 
Streptodonta, marine 
Tsenioglossa: 
Extra marine 
Pluviatile 
Docoglossa 
Rhipidoglossa: 
Marine 
Terrestrial 
Amphineura 
Solenoconcha 
Pelecypoda 
6 
8 
21, of which 2 are new. 
1, of which 1 is new. 
5 
2 
14 
76 
129, of which 15 are new. 
115, of which 9 are new. 
14 
2 
4 
42, of which 1 is new. 
10 
20, of which 1 is new. 
13 
171, of which 13 are new. 
Total 
653, of which 42 are new. 
