185G.] .. 63 



Descriptions of neic species of Gasteropoda from the Cretaceous formations of Xebraska 



Territory* 



By F. B. Meek and F. V. Haydex, M. D. 



The species indicated in the following paper comprise a portion of an extensive 

 collection recently brought from Nebraska hy one of the authors. f It is worthy 

 of note that some of the species contained in the collection from the most recent 

 Cretaceous beds of the upper Missouri country appear referable to genera which, 

 according to high European authority, date no farther back than the true chalk, 

 while many of them are closely analogous to Tertiary forms ; so close indeed, 

 that had they not been found associated in the same beds with Ammonites, 

 Scaphites and other genera everywhere regarded as having become extinct 

 at the close of the Cretaceous epoch, we would have considered them Tertiary 

 species. If these beds really are equivale it to any portion of the Green sand 

 of English geologists, it is a curious 'act that we should find mingled 

 together in tlieni upper Cretaceous and Tertiary forms exactly as if they 

 and those of the older Tertiary were deposited in the regular order of sequence. 

 Such facts however are sometimes met with amongst Pahtozoic formations. 



The following section exhibits the order of superposition of the formations in 

 which our Cretaceous fossils were found, and their relations to the Tertiary and 

 older rocks. 



Tertiary ( Beds of clay, sandstone, lignite, &c., containing remains of vertebrata, 

 400 to-! and at places, vast numbers of jilants, with land, fresh water, and 

 600 ft. (_ sometimes marine or estuary mollusca. 



5 ^ Gray and yellowish arenaceous clays containing great numbers of 

 marine mollusca with a few land plants. 100 to 150 feet. 





4 -J Plastic clays with numerous ^arine mollusca. About 350 feet. 



3 f Gray and yellowish calcareous 

 > \ scales, (fee. 100 to 150 feet. 



marl, containing Ostrea congesta, fish 



u 



2 \ Grayish and lead colored clays having few fossils. 80 feet. 



1 /Si; 



Sandstones and clays not positively known to belong to the Cretaceous 

 svstem. 90 feet. 



Limestones of upper coal measures at Council Bluffs, containing Spirifer 

 Meuscbachauus, AUorisma terminalis, Terebratula subtilita, Fusulina cylin- 

 drica, &c. 



ScALARiA CERETHiFORMis. Shell elougate-conical, turreted, not umbilicate; 

 volutions seven or eight, convex, closely contiguous, traversed by numeroussharp, 

 slightly curved cost*, less than the spaces between; surface marked by irregular 

 lines of growth, crossed by fine, unequal, thread-like, revolving lines, as strong 

 on the costte as between them ; suture distinct; aperture ovate, angular on the 

 inner sideabove, rounded below : lipthin, curved ontwardson the inncrside below. 

 Length 1.G5 inches, breadth .73 inch ; length of aperture .52 inch, breadth .40 

 inch ; apical angle slightly convex, divergence about 28. 



Locality. Moreau trading post. No. 5 of the series, rare. 



AcTEON suBELLiPTicus. Shell elougate-oval or narrow elliptical ; spire some- 

 what elevated; volutions about four; surfsxce polished, and ornamented by about 

 twenty-five regular revolving strite, composed of round punctfe so disposed as 

 to range up and down the shell exactly parallel to the obsolete lines of growth ; 

 suture distinct; aperture narrow, curved, acutely- angular on the inner side above, 



* Figures, comparisons, and remarks to be published hereafter, 

 f Dr. Hayden. 



