CONTRIBUTIONS TO INVERTEBRATE PALEONTOLOGY, NO. 3: 
Tria Ea eae MOLLUSCA FROM COLORADO, UTAH, AND 
By C. A. WHITE, M. D. 
The fossil mollusca herein described, and figured upon plate 13, have 
been collected at various times and by different persons connected with 
the two surveys which have heretofore been under the direction respect- 
ively of Dr. Hayden and Prof. Powell. Preliminary descriptions of all 
the species have before been published in different reports of those sur- 
veys, but none of them have before been figured. All the specimens 
figured on plate 13 are regarded as typical of the respective species, and 
the greater part of them are those from which the original descriptions 
were drawn. The type specimens—that is, those from which the origi- 
nal descriptions were drawn—have been used for illustration in all cases 
when they have been available; search for the types of a part of these 
species has, however, been hitherto unsuccessful, in consequence of their 
having been lost or mislaid. In these cases figures are given of speci- 
mens that have been carefully identified, and which have been collected 
from the same formations in which the original types were found, and 
at or near the original locality. 
All the species presented in this article are from the great fresh-water 
series of strata, which is usually, and doubtless correctly, referred to 
the Eocene Tertiary epoch, and which is divided into the Wahsatch, 
Green River, and Bridger Groups. There seems to be sufficient reasons 
of a physical character for dividing that great series of strata into the 
three subordinate groups just named, for purposes of stratigraphical 
study, but it is evident that a large proportion of the molluscan species 
which they contain are common to more than one, and in some eases at 
least, to all three, of the groups. The general characteristics of the inver- 
tebrate faunze of these groups is such also as to indicate their connection 
with, and proper reference to, a single epoch ; and such also as indicate 
not only a continuity of deposition over a very large area throughout 
the whole of the triple series, but also a continuity of existence of specific 
forms of molluscan life in the waters in which the whole of that con- 
tinuous deposition took place. 
CONCHIFERA. 
Genus UNIO Retzius. 
UNIO SHOSHONENSIS White. 
Plate 19, figs. 2 a and b. 
Unio shoshonensis White, 1876, Powell’s Rep. Geol. Uinta Mts., p. 126. 
Shell subelliptical in marginal outline; valves moderately and some- 
what regularly convex; test not massive; dorsal margin broadly convex; 
front margin regularly rounded; basal margin broadly and regularly 
convex; posterior margin somewhat abruptly rounded, the postero-dor- 
Al 
