74 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



V o D s c 1 1 a attenuata, M & H. 



Plate 28, figs. B, a, b. 



Mytilus attenuates, Meek and Haydeu (1856), Proceed. Acad. Nat. Sci. Pliilad., VIII, 86. 

 Modtola attenuata, Meek and Haydeu (1660), ib., xii, 127. 



Shell narrow, transversely elongate, nearly straight or but very slightly 

 arcuate, rather compressed ; anterior end narrow and compressed ; posterior 

 end wider, but rather narrowly rounded; hinge-line long and nearly parallel 

 to the longer axis of the shell; pallial border slightly concave; beaks nearly 

 terminal, small, compressed, and very oblique; surface unknown, but probably 

 smooth or only marked by lines of growth. 



Length, 1.90 inches; height at broadest part behind the middle, 0.58 

 inch ; convexity, about 0.40 inch. 



This species is more nearly like M. Meekii than any other known form 

 in the Nebraska rocks; but its much narrower and more elongated outline 

 smaller and much more compressed beaks, as well as its longer and less ob- 

 lique hinge, will prevent it from being confounded with that shell. 



It seems to be quite nearly allied to M. Hi/lanoides, d'Orbigny, as figured 

 by Chapuis and Dewalque, in Mem. Acad. Royal of Belgium, xxv, pi. 25, 

 fig. 6, but has a much longer hinge, and its anterior region is proportionally 

 narrower. In addition to these differences, the fact that it is an Upper Creta- 

 ceous species, and M. Hi/lanoides a Jurassic form, renders it scarcely possible 

 that they can be identical. It must be very rare, as we have seen but two 

 specimens of it. 



Locality and position. — Moreau River; from the Fox Hills group, or 

 formation No. 5 of the Upper Missouri Cretaceous : also from near the same 

 horizon on the Yellowstone River. 



Genus CRENELLA, Brown. 



Syiion.—Crenella, Brown (1827), Illnst. Conch., tab. xsxi; and Concb. Text-Book, 6th ed. (1845), 162.— 

 Gray (1842), Syn. Brit, Mus.,92.— G. B. Sowerbyjr. (1842), Conch. Man., 2d ed.72.— 

 Macgillv. (1843), Moll. Aberd. 205.— Lov<5u (1846), Ind. Moll. Scand., 32.— Gray (1847), 

 Zo61. Proa, 199. — H. and A. Adams (1857), Gen. Recent Moll., II, 514. 



Myoparo, Lea (1833), Contr. to Geol., 73.— Sowerbyjr. (1842), Conch. Man., 2d ed., 196. 



Stalagmium, Con. (1833), Fobs. Shells Tert., 39.— Broun (1838), Leth., 928.— Nyst. (1846), Fobs. 

 Belg.,238. 



ilodiotaria. Beck (1846), Mus. Hafn., ef. Auitl. Ber., 24.— Loven. (1846), Ind. Moll. Scand., 33.— 

 H. and A. Adams (1857), Gen. Recent Moll., II, 515 (as a subgenus under Crenella). 



Etym. — Cram, a notch. 

 Tiipt-.—Mijlilus decuasatus, Laskey. 



Shell equivalve, more or less inequilateral, suborbicular, subovate or 



