PALEONTOLOGY OF NEW-YORK. 
volume has been passing through the press, a careful review and re¬ 
examination of the specimens has enabled me to discover the existence 
of internal spires, which, from the displacement of those first examined, 
appeared to be arranged as in Atrypa; while farther examinations show 
that these appendages are arranged as in Spirifer and Trematospira. 
The T. globosa and T. formosa have so much resemblance to Retzia in 
general form and exterior markings, that they might readily be mistaken 
for species of that genus; but they have no area or extension of the 
hinge line, which is almost always conspicuous on the dorsal valve of 
Retzia. The shells of the latter are more finely striated and finely punc¬ 
tate throughout, while we are able to distinguish only a granular or 
punctate surface in Trematospira. 
In the United States, the Genus Retzia is yet unknown below the 
Carboniferous limestone. 
Had the materials now possessed been originally studied altogether, 
the whole, by some extension of the characters, might have been in¬ 
cluded in the same designation ; but it is only since the description of 
the genus has been printed, that I have obtained the means of showing 
the similarity of structure. 
The following species, except T. deweyi , differ from those already described, in 
being more extended like Rhynchonella , the beak strongly incurved, and the lateral 
slopes below the beak flattened or depressed as in that genus. 
The perforation of the beak, arrangement of the spire, and granular or apparent 
punctate structure of the shell of the following species, correspond with the pre¬ 
ceding species of Trematospira. The triangular depression beneath the beak, which 
in T. multistriata appears not to open into the cavity of the shell, is probably not a 
real character; since in these species it is clearly an opening into the interior, the 
beak of the dorsal valve being slightly inserted and held in place by a broad short 
cardinal process which is clasped at base by the cardinal teeth of the opposite valve. 
This intimate structure of the hinge has not been fully made out in the preceding 
species of Trematospira; and should it hereafter be found identical, the two groups 
may be united by some extension of the generic characters. 
From the general resemblance in external form and plicated surface of these 
shells to Rhynchonella , it is not improbable that some species referred to that genus 
may prove identical with those now under consideration. 
For illustrations of the internal structure of those species described 'on Plate 
xxxvi, and for T. rectirostra , see Plate xxxvi a. 
