BRACHIOPODA. 
133 
Neither can it be assigned to Orbiculoidea without opening that genus to the 
reception of heterogenous forms. For convenience, therefore, it is desirable to 
indicate the close but subordinate relations of this species* to Orbiculoidea, 
by the use of the new term (Ehlertella. 
The muscular impressions in Orbiculoidea are extremely faint and rarely 
discernible at all. We have seen no specimens showing them as clearly as the 
pedicle-valve of D. nitida, figured by Mr. Davidson and referred to above, where 
they are resolvable into anterior and posterior adductors, situated close together 
near the extremities of the pedicle-area, the posterior pair being at the distal 
extremities of long progressive scars radiating from near the apex. This 
arrangement of the scars indicates a general agreement with the muscular 
anatomy of Discinisca lamellosa. 
Orbiculoidea Randalli, Hall, a remarkably large species, known only from a 
single rather imperfect interior of the pedicle-valve, from the Hamilton group 
of New York, shows a slight median septum passing from the apex forward, 
comparable to that in Discinisca lamellosa; from this radiate a series of furrows, 
probably of vascular nature, which lie only within the inner lamellae of the shell, 
apparently not interrupting the external ornamentation. It will be interesting 
to learn whether this shell is congeneric with Orbiculoidea Morrisi , Davidson. 
Occasionally, in the brachial valves of American species, are seen two 
extremely faint ridges beginning near the apex and approaching each other at 
their anterior termination, nearly meeting the inconspicuous median septum. 
(See Plate IV f, fig. 22; also, Barrande’s figure of Discina reversa, Keyserling, 
Systeme Silurien, vol. v, pi. 95, fig I, 2 a.) In a large form from the Hamil¬ 
ton group of New York, usually confounded with 0. grandis, Vanuxem, these 
characters reach an extraordinary development and become most prominent 
features of the interior, beginning just in front of the apex, and, as they con- 
* The mode of preservation of this species frequently leads to deception in regard to its pedicle-charac¬ 
ters. When the two valves are preserved together, the breaking away of the upper portion of the larger 
valve often leaves its marginal portion surrounding the lower valve and closing the pedicle-aperture. In 
many such cases it is extremely difficult to distinguish the parts belonging to the respective valves on ac¬ 
count of the thinness of the shell, and we have taken pains to accumulate a very large representation of the 
species in order to fortify our conclusions. For much of the material at our disposal we are indebted to the 
favor of 'Professor C. L. Herrick, of Cincinnati. 
