OP CONCHOLOGY. 



PAIiiEONTOLOGICAL MISCELLANIES. 



BY T. A. CONRAD. 



Note on a Cretaceous limestone of Dakota. 



The Academy has received specimens of a black limestone 

 from Dakota, near Great Bend of the Missouri, where they were 

 found by Dr. Glatfelder. The surfaces of these fragments are 

 exceedingly irregular, and they are also full of cracks or seams 

 caused by the shells of Inocerami, and in some instances they 

 are almost composed of fragments of Inocerami, exhibiting their 

 peculiar fibrous structure. 



These shells are of two species, the I. Sagensis, of Owen, and 

 a smaller nearly smooth species, both in fragments. The rock 

 contains also entire specimens of a small Ostrea, and of a Lin- 

 gula, both shells having their valves united as when living. But 

 what is most remarkable of the Cretaceous rock of this age in 

 Dakota is the vast abundance of fragmentary Inocerami, proving 

 that shells of this genus must have in one stage of the Cretaceous 

 era actually paved the ocean bed. 



The fragments of these shells are of various sizes, and have 

 evidently been broken by agitation of the waters and attrition, 

 which have probably not been long continued, as the shell when 

 preserved, does not appear to be water worn, and the angles of 

 fracture are sharp. Dr. Leidy has a piece of English flint, on 

 the surface of which he pointed out similar fragments of an Ino- 

 ceramus imbedded in the centre of the mass. 



The most abundant determinable fragments of Inoeeramus^ a 

 few of which show a large portion of the shell and mould, appear 

 to belong to /. Sagensis, Owen, to which species I think should 

 be united /. Nehracensis, Owen, the only differences appearing 

 to be owing to age and "pressure. Both shells show on the mould 

 or cast, nnmerous radiating wrinkles. The agency of pressure, 

 in varying the form of a single species, is exhibited in /. proble- 

 maticus, a very abundant western species. 



