S64 
PALEONTOLOGY OF NEW-YORK. 
This arrangement leaves an enclosed triangular tube between the 
pseudo-deltidium and the converging dental plates. To these characters 
may be added the punctate texture of the shell, which, so far as now 
known, is accompanied in these forms by the external character and 
internal arrangements described. 
Besides these features, several.of our species have a median septum 
in the fissure, in continuation of the central septum below the 
junction of the dental plates. This septum is visible when the pseudo- 
deltidium is removed, as shown in figures of C. rostrata *, and as seen in 
many specimens of C. dalmani, as well as in C. biplicata and in C. hamil- 
tonensis. This central septum, both above and below the junction of the 
dental plates, may have the same origin : the coalescing of these 
plates allows the exterior laminae of each to unite, and extending inward 
form the septum dividing the cavity; while the inner walls of the dental 
plates are united and recurved, turning outwards to form the septum 
dividing the triangular space beneath the pseudo-deltidium. 
The several species which I have heretofore described as Cyrtia have 
all a punctate structure, and, so far as examined, they have the arrange¬ 
ment of the internal parts described in Cyrtina. It was not until after 
the completion of the third volume of the Palaeontology of New-York 
in 1859, that I received that part of Mr. Davidson’s Monograph of the 
Carboniferous fossils containing his arguments for the separation of the 
genera and his description of Cyrtina. The characters of Cyrtina, as 
given by Mr. Davidson, show its near relations with Spiriferina ; the 
principal differences, as illustrated in figures of the latter genus, being 
that the dental plates do not coalesce before reaching the bottom of the 
cavity, the high median septum rising unsupported nearly to the plane 
of the area. 
In that volume I have described two species under the name of Cyrtia, 
both of which have the structure of Cyrtina ; and in one of these I men¬ 
tioned the discovery of the spiresf, a feature which Mr. Davidson had not 
* Palaeontology of New-York, Vol. iii, pi. 96, f. 2 d, 3 a & 4 d. 
t Cyrtia rostrata , Pal. New-York, Vol. iii, p.429. 
