129 Bulletin American Museum of Natural History. [Vol. XXXIV, 
sediment, much of it relatively coarse, indicates a regular orogenic movement. 
Should this be the real cause of the faunal change, we may ask ourselves 
whether the dinosaurs did not perhaps persist to a still later period in the 
lowlands eastward, where conditions have not been so favorable for the 
preservation of their remains? 
Unio grangeri n. sp. 
Shell very large, thick and inflated, rather coarsely sculptured with growth lines, 
but without nodules or ridges; anterior end obtusely rounded; dentition very heavy; 
muscle-scars deep; pallial line deep anteriorly. Represented by both valves, which 
are however much broken, with the posterior end missing. As preserved, the length 
is 140 mm.; it was doubtless originally not less than 180; depth about 95 mm., and 
width in middle about 85 mm. The lower anterior part of the shell is 10 mm. or 
more thick, but posteriorly the shell is thinner, about 3 mm. near the broken hind 
— 
Pe — 
aoe e eee ; 
ae TEs 
Be et 8 : ! a 
| 
ec 
\ 
a 
My) yi) 
Fig. 1. Unio grangerin. sp. A, Dentition of right valve, from within; B, same from 
above. 
margin. The general outline is oblong, much as in Lampilis ligamentina (Lam.), 
but the swollen shell rather suggests L. ventricosa (Barnes). The umbones are not 
prominent (whatever sculpture they may have had is lost), and the dentition is of the 
Lampsilis type, with a very large thick posterior pseudocardinal on the right valve. 
The impression of the anterior retractor pedis muscle is large (14 mm. long) and very 
deep. It is fully 10 mm. distant from the upper end of the pallial line. 
Washakie, horizon B; Haystack Mts., Wyoming, north side, half way 
up, Sept. 20, 1906. (Paul Miller.) Named‘after Mr. Walter Granger, who 
has given us a good account of the Haystack Mtn. locality (Bull. Am. 
Mus. IN. ist, X XVI, pp. 13-93). 
This is probably a Lampsilis. Its great size and ventricose form readily 
distinguish it from previously described Tertiary Unionide of the Rocky 
Mountains. 
