' TRENTON LIMESTONE. 151 



190. 2. NUCULA POSTSTRIATA. 



Tl. XXXIV. Figs. 2 o, 6. 

 % t 



A'ucuUtes poststriata. Emmons, Geol. Report, 1&4'2, pag. 399, fig. 4. 



Oblong-, somewhat quadrangular, compressed ; extremities of nearly equal widtii ; 

 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 (he 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 TELLING MYA. 



[ From Tellina and Mya, 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 sny 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. 



