73 
CRETACEOUS INVERTEBRATES 
By F. H . McLearn , Geological Survey , Canada 
Illustrations 
Plates XII1-XIX. Illustrations of fossils 
Page 
133-145 
As the succession and correlation of the Cretaceous faunas are con- 
sidered in the succeeding section, there only remains the description of 
new species. Dr. T. W. Stanton has given most helpful advice, particu- 
larly in the interpretation of the Blairmore and Lower Allison pelecypods. 
Dr. J. B. Reesidfc, jun., has aided in the study of Scaphites. 
BLAIRMORE SPECIES 
Unio natosini n.sp. 
Plate XIII, figures 7-9 
Shell rather small, moderately convex, longer than high, and appar- 
ently a little higher at the posterior end than at the anterior. Rounded, 
postumbonal slope. Broadly concave between postumbonal slope and 
dorsal margin. Umbones not very prominent and near the anterior end. 
Dorsal margin imperfectly preserved, apparently somewhat shorter than 
the ventral margin. Anterior margin rounded. Posterior margin appar- 
ently sub truncate above. 
The ornament can be better illustrated than described. It consists 
principally of curving lines of tubercles, although in places there are curving 
costae bearing tubercles. On the umbo the tubercles are arranged in 
V-shaped rows, but ventrally the apex of the V becomes rounded and the 
tubercles are in irregular curves or festoons. Posteriorly they curve 
upward to the postumbonal slope. There they bend back on themselves 
so that above the postumbonal slope they are directed upward and anter- 
iorly. They are not very distinct there in the Blairmore specimen pre- 
serving this part of the shell, but appear to be more pronounced in the 
Harlowton specimens. Above the postumbonal slope are curving cost® 
with tubercles directed postero-dorsally; these are least marked on the 
Blairmore specimen showing this part of the shell. 
The name is given for Natosin, a chief of the North Blackfeet Indians. 
Length 50 mm., height 35 mm. 
Horizon and Locality . In the Blairmore formation, about 230 feet 
above the base on Lyon creek, Blairmore map-area, Alberta, and in the 
Kootenai formation, about 6 miles south of Harlowton, Montana. 
Types. National Museum of Canada; holotype, Cat. No. 9028; 
paratype, Cat. No. 9028a. XJ.S. National Museum; paratype. 
Unio hamili n. sp. 
Plate XIII, figures 1-4; Plate XIV, figure 6 
Moderately convex, longer than high, and narrowed posteriorly. 
Ventral margin broadly rounded, merging into the rounded anterior 
margin and the short, obliquely truncated posterior margin ; dorsal margin 
