C. A. White—Fresh-water and Land Mollusca. 47 
ever, indicate that a wide differentiation had taken place in the 
Pupine at that early time. Pupa arenula and P. atavuncula 
White, discovered in the Green River strata of Wyoming, are 
referred provisionally to Pupzlla, and an associated species Pupa 
encolata White, to Lucocheila. Mr. Meek referred his Pupa 
Leidyi doubtfully to Holospira. It is from the Bridger strata of 
Wyoming. 
Only one species of the Succinine has yet been discovered in 
any of the strata here considered, namely, Succinea papillispira 
of the Green River strata of Wyoming. This is plainly refera- 
ble to Brachyspira. 
The Unionide of the fossil molluscan faunz, herein dis- 
cussed, are found to have become differentiated to a remarka- 
ble extent, especially during the Laramie epoch. An exceed- 
ingly interesting and suggestive fact in connection with this 
differentiation is that the subordinate types are largely indenti- 
cal in character with some of those which are now living in the 
waters of the Mississippi River system, and which are recog- 
nized by malacologists as distinctively North American types. 
Illustrative of this relation of the fossil to the recent forms, the 
following parallel lists are presented, those of the left-hand col- 
umn being a part of the fossil species now known in the Lara- 
mie strata of Wyoming and Utah; and those of the right-hand 
column being the living species of the Mississippi River system 
which are selected as their respective type-congeners. 
Unio propheticus White. — - U. clavus Lamarck. 
U. proavitus W. U. ridibundus Say. 
U. ‘ U. multiplicatus Lea. 
U. holmesianus W. U. apiculatus Say 
U. Coue yplanatus Solander. 
U. Endli ‘ U. rnes. 
U. brachyopisthus W. U. circulus Lea. 
Still other examples might be given of close resemblances 
between fossil and recent forms of Unio, but these suffice to sug- 
gest, In a very forcible manner, that the Unione fauna of the 
Mississippi River system is genetically related to that of the 
Laramie period. It is true that in the Laramie fauna there are 
