1915.]| Cockerell, New Fossil Species of Unio. 125 
growth-lines distinct, but no ridges or nodules. Length 69.5 mm.; height 44; 
breadth about 27 mm.; length of hinge-lamelle about 28 mm.; level of umbones 
(vertically) from level of anterior margin about 21 mm.; anterior end of pallial line 
from margin of shell 8.25, from anterior retractor pedis 4 mm. ; width of scar of poste- 
rior adductor 10.5 mm. Seen from above, the lateral outline of the anterior end of 
the shell is entirely convex, without the flattening due to compression which is con- 
spicuous in U. sinope. 
Wasatch Eocene, Gray Bull beds; north side of Dorsey Creek, nine 
miles from St. Joe, Big Horn Basin, Wyo. (G. Olsen, October byeT9u1). 
Found with a quantity of U. wasatchensis, from which it is readily known 
by the thick shell and heavy dentition. The umbones are less prominent 
than in U. shoshonensis, but the dorsal margin is convex as in that species. 
Unio sinope n. sp. 
Shell thick, with very heavy, broad dentition; growth lines strong, but no 
nodules or ridges; umbones too worn to show any sculpture; anterior end com- 
pressed, so that when seen from above the anterior lateral outline is slightly concave 
4. | |. e(t valvs. 
Fig. 4. Unio sinope n. sp. A, Dentition of left valve, from within; B, same from 
above; C, anterior end, from above. 
a short distance behind the margin. Umbones about 35 mm. from anterior margin; 
pallial line weak, its anterior end 14 mm. from margin; anterior margin broadly 
rounded. The shell is represented only by the anterior and middle parts, but it 
evidently was over 100 mm. long und somewhat over 50 deep. The dentition (left 
valve), with a large subquadrate fossa between the pseudocardinals, is quite dis- 
tinctive. : 
Wasatch Eocene; North side Dorsey Creek, 9 miles from St. Joe, Big 
Horn Basin, Wyo. (G. Olsen, October 1, 1911). Gray Bull beds. Found 
with U. wasatchensis. 
