S9Q 



PALEONTOLOGY OF NEW YORK. 



the expansion terminating abruptly above, and, from its outer angle, the minute 

 spino proceeds like the mucronate extension from the points of the serraturos in 

 some graptolites. 



This form differs from the strict description of Rastrites, in having the stipe much 

 larger than the cellules. Whether these points or processes are the true cellules, or 

 extensions from them, might admit of some doubt, were observations based upon 

 this species alone. 



Kastrites barrandi. 



Fig. 1. View of the specimen, natural size. 

 Fig. 2. A part of the same enlarged. 



Geological position and locality. In the shales of the Hudson-river group 

 Albany. Collected by Mr. R. P. Whitfield. 



Near 



OeNVS TrIPLESIA ( Hall, 1858 ). 

 [ (jr. TpiirXaaio^, triplex, in reference to the trilobate character of several of the species.] 



Shells transverse or elongate, trilobate or subtrilobate ; the ventral valve 

 being marked by a broad deep sinuosity, and the dorsal valve by a 

 corresponding fold. Hinge-line straight : area small ; foramen triangu- 

 lar. External surface concentrically striated, and with fine obscure or 

 obsolete radiating striae : internal structure not determined. 

 I have proposed this name to include Jltrypa extans, A. cuspidata and A. nucleata 

 of Vol. i, Palaeontology of New-York, as well as other species. An examination of 

 Atrypa extans has shown the existence of a narrow area and small triangular fora- 

 men, as in Spirifer; but I have not been able, thus far, to determine the internal 

 structure. The texture of the shell, and surface marking, although differing in some 

 particulars from those of Merista, are nevertheless similar. 



