- 
TRENTON LIMESTONE. 155 
The three following species are of forms which have heretofore been referred to the genera 
Cypricarpia, Carpium, &c.; but I am satisfied that this is an improper reference, and that 
the shells have not the characters of these genera. They approach more nearly to Saxicava 
and VENERIRUPIS among recent shelis, but they differ from any of these. The reference of 
Silurian fossils to Cypricarp1a should be regarded with distrust, since species of that genus 
are so rare among recent shells, and all the fossil species yet referred to it are of Silurian, 
Devonian or Carboniferous age ; while during the long interval between the latter period 
and the present, the genus has been absent from the fauna of the globe. 
The most obvious characters of the following species will be found in the rigid straight 
hinge line, like CucutieEa, with the umbones placed near to, or over, the anterior extremity, 
which, in most instances, is abruptly rounded. Shells often very gibbous. 
M. ve Verneuit has suggested to the Author, that several of these will fall under the 
genus Edmondia of pe Konincx. Not being able fully to ascertain the characters on which 
this genus is founded, I place them with some hesitation under that name. It may probably 
be found hereafter that they will require a separation from this genus. 
197, 1. EDMONDIA VENTRICOSA (n. sp.). 
Pu. XXXV. Figs. 1 a, b, ¢, d, e, f. 
Rhomboidal, cuneate, ventricose above, with the umbones large and prominent, and 
almost in a line with the anterior margin of the shell ; cardinal line short, from the posterior 
extremity of which the shell slopes abruptly towards the ventral margin ; posterior dorsal 
margin compressed ; anterior extremity obtuse ; posterior extremity acute, cuneate ; surface 
with fine concentric strie. 
Nearly all the specimens seen are casts, with the surface markings more or less obscure 
or exfoliated. By placing the posterior extremity downwards, the shell is obtusely cuneate, 
diminishing rapidly in that direction. The specimens usually found are casts, and suffer 
various distortions from compression in different directions, giving, in some instances, a 
widely different form to the shell. Anterior profile cordiform, 
. 1 a. Right valve of a large and perfect specimen. 
1b. Anterior extremity of the same, showing the ventricose character of the shell. 
1c. Dorsal view of the same. 
. 1 d. Left valve of a smaller individual. 
ig. 1 e. Left valve of a specimen which has been compressed vertically, and is covered by a fine striated 
lamina of shale.* 
Fig. 1 f- Dorsal view of the same. 
The proportions of length and breadth in this specimen are greatly altered by compression, 
the umbones depressed, and the length of the shell apparently increased. 
uQ” 0g” 03° 09 
rey be bof 
Position and locality. In the central and higher part of the Trenton limestone at Middle- 
ville, Herkimer, Trenton Falls, Lowville, and other places. (State Collection.) 
20* 
