522 
PALAEONTOLOGY OF NEW-YORK. 
the expansion terminating abruptly above, and, from its outer angle, the minute 
spine proceeds like the mucronate extension from the points of the serratures in 
some graptolites. * 
This form differs from the strict description of Bast-rites , 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. 
Rnstrites barrandi. 
1 
l 
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 : Near 
Albany. Collected by Mr. R. P. Whitfield. 
OENUS TkIPLESIA ( Hall, 1858 ). 
[ Gr. TpinXaaiotriplex, 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 Atrypa extans , A. cuspidata and A. nucleata 
of Yol. i, Palseontology 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. 
