218 
PALAEONTOLOGY OF NEW-YORK. 
Nucleospira. 
In Murchison’s Silurian System, Mr. Sowerby lias' described, under the 
name Spirifer? pisum, a species differing essentially in general external 
characters from the typical forms of that genus. This species has been 
adopted as a true Spirifer in Morris’s Catalogue of British Fossils, and 
in the Nomenclator Palaeontologicus of Bronn, as well as elsewhere. 
Subsequently I discovered in the Niagara shales a form so similar to the 
British species, that I regarded it as identical; but, from the condition 
and character of the specimens, I considered them as more nearly allied 
to Orthis than to Spirifer, and, accordingly, in the second volume of the 
Palaeontology of New-York, designated the Niagara fossil Orthis pisum. 
Since that period, my collections from the Helderberg have revealed a 
species similar to the one from the Niagara group; but among the numerous 
individuals from the latter rocks, I found several which were clearly 
furnished with internal spires like the true Spirifer, thus separating it 
from Orthis by unequivocal characters. Finding no genus for the reception 
of these forms, I described the latter as Spirifer ventricosa; and it has. 
been so published in my descriptions of new palaeozoic fossils in the 
Report of the Regents of the University upon the State Collections of 
Natural History. 
Farther examination has satisfied me of the impropriety of placing 
this fossil under either of the genera named, for several reasons. The 
central depressed line, or narrow sinus, which might be regarded as the 
mesial sinus of Spirifer, is almost equally a character of both valves; the 
apparent area is not a true area; and the apparent foramen, being merely 
a depression in the false area, does not correspond to the foramen either 
of Spirifer or of Orthis, not opening into the cavity of the shell. The 
hinge line is not extended in the manner of these shells, particularly of 
the former; while the presence of a spire sufficiently distinguishes it 
from the latter. 
The Lower Helderberg group furnishes one, and perhaps two, other 
