XVII. 



Descriptions of Neio Sj)ecics of Fossils, from the Cretaceous Formations of Nebraska, 

 %vith Observations tipon Baculites ovatus and B. coJirRESsus, and the Progressive 

 Development of the Septa in Baculites, Ammonites, and Scaphites. 



By JAMES HALL and F. B. MEEK. 



{Communicated June 27, 1854.) 



The collections which have furnished the following new species from the cretaceous 

 formation of the Upper Missouri, were made in the summer of 1853, by Mr. F. B. 

 Meek and F. V. Hayden. The collection of Mammalian remains from the Tertiary 

 period has been placed at the disposal of Professor Leidy, for his forthcoming new 

 memoir upon the fossil remains of that region. 



Callianassa Danai, n. sp. (Fragment.) 

 Plate I. Fig. 1, a, h. 



Exterior surface convex, inner surface flat, upper and lower edges obtusely angular ; 

 fingers nearly as long as the hand ; upper one nearly triangular in section and de- 

 pressed above near its articulation, and marked along its upper edge at regular intervals 

 by four small foramina, outer side depressed above the middle and towards the lower 

 margin, and marked by two large foramina, dividing the whole into three nearly equal 

 spaces ; upper angle obtuse, lower edge sharp and smooth, arcuate from the apex back 

 a little more than half the distance to the base, from which point it curves again 

 towards the articulating extremity, lea\ing the widest part near the middle. Lower 

 finger narrower than the upper, equal in lengtli, bending slightly downwards from 

 the hand, and thence gradually curving upwards to the extremity, marked on the 

 upper slope of the outer angle by two foramina, one near the base and one near the 



