Logan.] The Invertebrates, Niobrara Group. 485 



condition may be accidental. The specimen was collected from 



the Ornithostoma beds on the Smoky Hill river, south of Gove 



City. 



MOLLUSCA. 



Ostrea (Alectronia) larva Lamarck. 



Ostrea falcata Morton, Syn. Org. Rem. Cret. Group, p. 51, pis. in, ix; White, 



1884, 4th Ann. Rep. U. S. Geol. Surv., p. 294, pi. xxxix, ff. 11, 12, 13. 

 Ostrea mesenterica Morton, ibid.; White, ibid. 

 Ostrea nasuta Morton, ibid.; White, ibid. 

 Ostrea larva Lamarck, A. S. V., vol. vi, p. 216; White, ibid. 



Description : Shell small, narrow, subelliptical in general 

 shape, diminishing in size posteriorly ; posterior dorsal margin 

 deeply crenate or toothed ; anterior ventral margin slightly 

 toothed ; exterior of shell in some specimens showing lines of 

 growth, in others smooth ; interior smooth ; beak obliquely 

 rounded ; umbonal slope abrupt ; hinge line short, almost 

 straight, placed tangentially to the rounded beak. 



Length, following central line of curvature, thirty mm. ; 

 breadth in antero-central region, ten mm. ; height of longest 

 tooth, five mm. 



The margins of the two shells when they are fitted together 

 form a zigzag line. This line diminishes in the length of its 

 excursions from a central line as each end of the shell is ap- 

 proached. The distance between the lines of the excursions 

 remains nearly constant. All of the varieties represented by 

 Doctor White's figures in the Fourth Annual Report of the 

 United States Geological Survey are represented in the Univer- 

 sity collection. These forms represent Morton's three varieties 

 — falcata, mesenterica, and nasuta. 



Ostrea larva occurs in both the Hesperornis and the Rudistes 

 beds of the Niobrara Cretaceous, but specimens are not abun- 

 dant. 



Inoceramtis flaccidus White. Plate xc. 



Inoceramus flaccidus White, 1876, U. S. Geog. and Geol. Surv. West of the 

 100th Mer., vol. iv, p. 187, pi. xvi, ff. la, b; Stanton, 1893, Bull. U. S. 

 Geol. Surv. No. 106, p. 80, pi. xin, f. 1. 



Original description: "Shell large, irregularly subovate in 

 marginal outline, exclusive of the ears ; valves subequal, not 



