56.43 (118:73W) 
Article III— GASTROPOD MOLLUSCA FROM THE TERTIARY 
STRATA OF THE WEST. 
By F, 1D, A. Cockere.i.. 
A study of the Land and Freshwater Mollusca of the Rocky Mountain 
. Tertiary strata leads to the expected conclusion that freshwater species 
have a greater range in time than terrestrial ones. More careful analysis 
of the evidence, however, indicates that this opinion is not so well supported 
as it at first seems to be. Successive groups of strata will contain repre- 
sentatives of the same genera of freshwater shells, while the land shell 
fauna found will usually show much generic diversity from period to period, 
in spite of the fact that most of the genera concerned have persisted down to 
the present day. This means, of course, that the terrestrial forms, though 
probably more numerous and diversified than the aquatic, are not so likely 
to be.preserved. Thus we have in many cases a fairly representative show- 
ing of the freshwater genera, but only odds and ends of the terrestrial series. 
It must also be noted that freshwater forms often fail to show very 
marked external features distinguishing allied species, and it is always 
possible that apparently long-lived types may in reality be composite, 
although we are not able to divide the material before us. 
Three species of Vivparus, represented in the material before me, 
appear to extend from the Paleocene (whence they were described) well 
into the Eocene. 
(1.) V. trochiformis (Meek & Hayden). Torrejon Formation, East 
Fork Torrejon Arroyo, New Mexico (Am. Mus. Nat. Hist., Exp. 1913); 
and also from the Wasatch at Ojo San José, New Mexico, many specimens 
(Stein; July 11, 1912). 
(2.) V. letdyi (Meek & Hayden). Three lots from Clark’s Fork Basin, 
Wyo., in the Sand Coulee Beds, collected by Granger and Stein. Three 
miles east, three miles southeast, and five miles southeast of the mouth of 
Pat O’Hara Creek. + 
One of the last lot is large, with aperture preserved; it is remarkable 
for the long aperture, which at once distinguishes it from V. wyomingensis. 
Aperture 23.5 mm. long; top of aperture to apex of spire 17.5 mm.; same 
length of spire on central axis 14.5 mm. Upper whorls only slightly convex. 
(3.) V. retusus (Meek & Hayden). Many specimens, not very well 
preserved, from San Coulee Beds, head of Big Sand Coulee, Wyo. aariger 
and Stein, Sept. 9, 1912). 
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