INVERTEBRATE PALEONTOLOGY. 43 



as figured by Groldfuss (Petrefact. Genu., tab., cxv, fig. 1). The beaks, how- 

 ever, are not so distinctly curved forward as in the latter species, and the 

 posterior and basal borders form a more regular curve. 



Dr. Zittel, in his valuable Monograph of the Bivalves of (he Gosau 

 Formation, cites /. fragilis, Hall and Meek, as a synonym of I. Cripsii, 

 Mantell. This, however, is an error; I. fragilis being a typical Inoceramus, 

 while I. Cripsii belongs to the Catillus section, and is, of course, widely 

 distinct specifically. 



Locality and position. — The original typical specimen of this species 

 was found near the mouth of Vermillion River, on the Missouri, at or near the 

 base of the Fort Benton group, where it was associated with Ammortitrs 

 percarinatus, H. and M. The specimen represented by our fig. o, pi. 5, came 

 from near the same locality ; while the larger ones, from which our wood- 

 cuts were prepared, came from the same horizon near Fort Benton, Montana. 

 We also have it from the same rock in the Black Hills ; and Dr. Newberry 

 found it in ecpiivalent beds in New Mexico. 



Inoccramus altus, M. 



Plate 14, figs. 1, a, b. 

 Inoccramus altus, Meek (1871), Dr. Hayden's Report Geol. Survey of the Territories, 302. 



Shell attaining a medium size, vertically or a little obliquely subovate, 

 being in the adult higher than long, and widening from the hinge downward, 

 moderately convex, equivalve, very inequilateral; hinge very short and rang- 

 ing nearly at right angles to the longer axis in the adult, but a little more 

 oblique in young shells ; anterior side straight, long, and truncated vertically, 

 or nearly at right angles to the hinge, immediately in front of the beaks ; 

 base regularly rounded ; posterior outline forming a broad, somewhat oblique, 

 gentle curve from the posterior end of the hinge into the base; beaks nearly 

 or quite equal, rising little above the binge-line, pointed, obliquely incurved, 

 and placed immediately over the anterior margin. Surface of cast showing 

 more or less regular, rather obscure concentric undulations, and faint traces 

 of radiating markings ; the latter probably not being defined on the exterior. 



Height, about 6.50 inches; length, about 4.90 inches ; convexity, "2.70 

 inches; length of hinge, about 2.40 inches. 



This species seems to belong to the typical section of the genus, but, 

 like the last, it presents the rather unusual character of having its beaks 



