144 The American Geologist. March, i904. 
or belated. The number of species known at present between the begin- 
ning of the Oligocene and the present fauna is between three and four 
thousand, probably less than half as many as will eventually be obtained 
and discriminated. 
"In the course of the work it became necessary to consider the sys- 
tematic arrangement of the Pelecypoda. The general subject ' required 
revision in the light of recent researches, both in anatomy and paleon- 
tology. With this view Part III. was devoted to a compilation of ex- 
isting data, in which material from many sources was brought together 
and an approximate classification deduced." 
The class Pelecypoda is here divided into the orders : I. 
Prionodesmacea (subdivided into lo super families and 34 
families) ; II, Anomalodesmacea (3 superfamilies and 15 fam- 
ilies) ; and III, Teleodesmacea (17 superfamilies and 46 fam- 
ilies). 
"In the earlier part of the work it was recognized that the so-called 
Miocene of Florida comprised two very dissimilar faunas, and to the 
earlier the term Old Miocene was applied in this work. Further study 
and material showed that this "Old Miocene" had nothing to do with 
the Miocene of the United States in its most typical development, as in . 
Virginia and Maryland, but represented a group of horizons strictly 
analogous to those which had received from European geologists the 
name of Oligocene. 
"These horizons contained a very rich warm-water fauna which was 
soon found to be more or less distinctly represented in the Tertiaries 
of Middle America and the West Indian Islands. This fauna then had 
to be examined and collections made at Bow^den. Jamaica, and other 
important points in order that the correlation of the Antillean and con- 
tinental beds might be discovered and duplication of descriptions avoided. 
It was found that the connection between the Atlantic and Pacific faunas 
ceased at about the climax of the Oligocene, and that the relations be- 
tween the faunas were so intimate that the Pacific coast forms could not 
safely be entirely neglected. This conditon of things will account for 
the references to faunas not strictly Floridian, of which this work con- 
tains so many, yet which were essential to the proper understanding of 
both the paleontological and geological evolution of the region con- 
cerned. 
"Among other things accomplished, several distinct Oligocene faunas 
have been worked out with fullness and .their relations established ; a 
wide extension has been given to the Pliocene deposits, long confused 
with those of the upper Miocene ; the geological relations of the beds be- 
tween the Vicksburgian and the Pleistocene have been established in 
their main lines more clearly than has hitherto been the case in the 
region studied; the species of half a dozen faunas have been revised, 
their nomenclature modernized, many new forms recognized, described, 
and figured; old confusions have been cleared up, old errors rectified, 
and a substantial advance in the Tertiary paleontology of our south- 
•eastern coastal plain has been secured. 
