Log an. J The Invertebrates, Benton Group. 455 



bring its point near the anterior margin ; surface of cast smooth , 

 or marked by obscure concentric undulations. Length from 

 anterior to posterior margin, ten cm. ; height, fourteen cm. ; 

 convexity, seven cm." 



The casts of two valves of this species were obtained from the 

 Fort Benton limestone. The twisted beak precludes the possi- 

 bility of its belonging to /. umbonatus , as suggested by Stanton. 

 ( See citation above.) 



Inoceramus tenuirostratus M. & H. Plate xcv, figs. 3, 4. 



Inoceramus tenuirostratus M. & H., 1862, Proc. Acad. Nat. Sci. Phil., p. 27; 



Stanton, 1892, Bull. U. S. Geol. Surv. No. 106, p. 83, pi. xvi, ff. 3, 4. 

 Inoceramus tenuirostris Meek, 1876, U. S. Geol. Surv. Terr., vol. ix, p. 59, 



f . 5 in text. 



Stanton's revised description: "Left valve very gibbous, 

 subquadrate in outline ; anterior margin very short or verti- 

 cally truncated, with a slightly convex outline, immediately in 

 front of the beak, and rounded into the base below ; ventral 

 margin nearly semi-elliptical ; posterior side rounded, or some- 

 times subtruncated, with a slightly convex outline above, and a 

 little more prominent and rounded into the base below ; hinge 

 of moderate length, with cartilage furrows small, there being 

 about five of them in the space of twenty-hundreths inch ; beak 

 very gibbous, prominent, narrowed, strongly incurved, and di- 

 rected a little forward, its point being directly over the anterior 

 region. Surface of internal cast smooth over the gibbous um- 

 bonal region, but showing traces of small, concentric undulations 

 below the middle. Length, 2.10 inches; height from the base 

 to hinge, 1.82 inches ; height to tip of umbo, 2.13 inches ; con- 

 vexity of left valve, .90 inch." 



A few specimens of this species have been collected from the 

 Septaria horizon of the Fort Benton formation. 



Inoceramus undabundus M. & H. Plate xcv, figs. 1, 2. 



Inoceramus undabundus M. & H., 1862, Proc. Acad. Nat. Sci. Phil., p. 26; 

 Meek, 1876, U. S. Geol. Surv. Terr., vol. ix, p. 60, pi. in, ff. 2a, b; Stanton, 

 1892, Bull. U. S. Geol. Surv. No. 106, p. 84, pi. xvi, ff. 1 and 2. 



" Shell obliquely rhombic subovate or subquadrate, gibbous ; 

 anterior side very short, and rounding obliquely downward into 



