354 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
references only, without any attempt at synonymy, were given for all citations of 
species supposed to be from the West Indies and adjacent shores. Considerable 
additions have since been made in the Blake Reports, the Proceedings of the United 
States National Museum, the Nautilus, and elsewhere. A supplement to the bulletin 
referred to, which should include the species cited from this region in the iconog- 
raphies and the later issues of the periodicals mentioned, would be of immense 
service in helping to bring order out of the existing chaos. 
Meanwhile all carefully determined lists of species from definite localities are of 
the utmost value, and only when a large number of these have been made can we 
expect to utilize the facts of inter-island or bathymetric distribution. The present 
report is intended to be of this character. Great care has been taken to identify the 
species correctly, while the question of ultimate nomenclature has in great part been 
left in abeyance. It is believed that the names assigned in every case belong to the 
species designated; but whether in all cases the designation used is the first which 
was ever applied to the species in question we have not attempted to determine, 
though in most cases it is believed to be so. 
At the request of the authorities of the Commission, who hoped this report 
might be to some extent utilized as a handbook for the mollusks of the island, a 
brief description has been prepared by Mr. Simpson of the genera, subgenera, and 
species present in the collection. This has been a work of considerable magni- 
tude and has occupied a great deal of time. The portion of this report relating to 
the land shells is entirely the work of Mr. Simpson, who has also had the task of 
compiling the list of species not represented in the Fish Commission collection. The 
work of the senior author has been chiefly devoted to the revision and verification of 
references, the confirmation of the identifications of the marine forms, the descrip- 
tion of new marine species, and general editorial supervision. 
Our intention has been to give a reference to the place where a species was 
originally described, and to a figure, without attempting elaborate synonymy. Sev- 
eral species hitherto unfigured, though described half a century ago, have now been 
figured from the author’s types. Nearly all the new species ai’e figured, and also a 
few forms not new or unfigured, but which are especially characteristic of this island, 
such as Pleurodonte carocolla. 
It has been one of the surprises that a number of species originally described 
from deep water in the Blake Reports turned up in less than 100 fathoms in 
Mayaguez Harbor or other localities. It is evident that a thorough exploration 
with the mollusks especially in view, and systematically conducted dredgings, would 
add very materially to the list now presented. 
In a discussion of the number of marine species normal to a fauna in a given zone 
of temperature 1 the conclusion was arrived at that, omitting strictly abyssal species, 
the average marine American tropical shell-fauna comprises about 581 species, and, 
as none of the faunas cited could be regarded as thoroughly known, it would doubt- 
less be well within the mark to call it in a round number 600 species. 
Porto Rico has a sufficient variety of coast, with rocks, flats, sheltered harbors, 
currents, and submarine declivities, to sustain a fully average representation of the 
1 Bulletin of the U. S. Geological Survey No. 84. Correlation Papers. Neocene, by William Healey Dali and Gil- 
bert Dennison Harris. Washington (the Survey), 1892. 8°. pp. 349. See pp. 25-31. 
