TRENTON LIMESTONE. 
151 
190. 2. NUCULA POSTSTRIATA. 
Pl. XXXIV. Figs. 2 a, b. 
JSfuculites poststriata. Emmons, Geol. Report, 1342, pag. 399, fig. 4. 
Oblong, somewhat quadrangular, compressed ; extremities of nearly equal width ; 
anterior extremity rounded, posterior one obliquely truncated ; umbones compressed, sharp, 
with an angular elevation extending obliquely to the posterior basal margin ; posterior 
slope strongly striated with diverging elevated lines ; remainder of the shell apparently 
smooth. 
I have referred this specimen, with some hesitation, to the Genus Nucula, having seen 
no evidence of crenulations on the hinge line, and the strong striae upon the posterior slope 
are characters not usual in species of this genus. 
The species under consideration is rare in the Trenton limestone, and has heretofore been 
regarded as belonging to the Hudson-river group, where it is more frequently seen, and 
where it attains a larger size ; but since I have adopted the invariable rule of giving the 
species where it first appears, this one is presented here. 
Fig. 2 a. Right valve of this species, b. Cardinal view of the same specimen. 
Position and locality. In the compact part of the Trenton limestone, associated with 
several other species of shells peculiar to the rock. Carlisle, Pa. 
Genus TELLINOMYA. 
[ From Tellina and My a, from the form of the shell.] 
Character. Equivalve, inequilateral, somewhat compressed below, but becoming gibbous 
at the umbones ; umbones not angular ; outline of the shell curved, without angular ridges ; 
shell thin, closely laminated ; hinge without visible teeth or crenulations ; muscular 
impressions two in each valve, near the dorsal margin ; often apparently gaping at the 
posterior extremity. T. nasuta. 
This is one of several fossil shells of the Acephalous Mollusca, in the Trenton limestone, 
which cannot be satisfactorily referred to any of the existing or fossil genera with which I 
am acquainted. It is with great diffidence, however, that I propose a generic designation 
for it; being willing to avoid, if possible, the multiplication of names, where the continuance 
of previous ones, or the reference to recent genera, will not produce confusion. 
I am well aware of the difficulty, not to say impossibility, of properly characterizing a 
genus, where the specimens are in the condition of these ancient fossils ; and, therefore, 
general external form, and the structure of the shell, must be allowed some weight. In the 
present instance, the form of the shell, and some other characters in the typical species, are 
so widely different that they cannot fail to arrest attention. 
