BRACHIOPODA. 443 
Orlhis (DaliiiatioUa) tesl iidhiaria .1 
than twice the size], suboval in form and extending to near the middle of the valve; 
cardinal process very small [comparatively large, striated] and trifid; brachial pro- 
cesses comparatively rather stout and prominent; internal surface having the radi- 
ating stria? of the exterior rather distinctly impressed through, as it were [each 
with a central furrow], in consequence of the thinness of the shell, and finely 
granular, the granules being apparently connected with the punctate structure of 
the shell. 
"Ventral valve compressed-convex, the greatest convexity being near, or a little 
behind, the middle, along a more or less prominent, undefined ridge that sometimes, 
but not always, imparts a subcarinate appearance to the central and umbonal 
regions; beak small, projecting somewhat beyond that of the other valve, abruptly 
pointed and rather distinctly arched, but not strongly incurved; area about twice as 
high as that of the other valve and with its sharply defined edges sloping to the 
lateral extremities of the hinge, directed and arched obliquely backward with the 
beak; foramen [delthyrium] having nearly the form of an equilateral triangle, but 
rather narrowed upward to the apex of the beak [with a distinct linear ridge along 
each w^all] and partly occupied by the cardinal process of the other valve. Interior 
showing the teeth to be moderately prominent; concavity for the muscular impres- 
sions very shallow, somewhat bifid anteriorly and not defined by a very distinct 
marginal ridge; at the base of the dental plates are situated the narrow adjuster 
scars, terminating at the transversely striated pedicle muscle, which occupies the 
posterior portion of the rostral cavity; on the inside of the former are the large 
diductors separated by the small, elongate adductors; striae and fine granules of the 
interior as in the other valve. 
"Surface of both valves ornamented by numerous, distinct radiating strife that 
usually bifurcate about three times between the beak and free margins; posterior 
lateral stria3 so strongly curved that a part of them run out on the hinge-line. 
Numerous very minute, regularly disposed, concentric lines may also be seen by 
the aid of a magnifier, most distinctly defined in the furrows between the radiatiug 
striae, while a few distinct, subimbricating, stronger marks of growth are usually 
seen in adult shells." Shell structure distinctly punctate. 
Size of shell, outline, convexity of valves and number of striae are more or less 
variable features at all localities of this species. "The shells of this species usually 
characterize the Trenton and Hudson River beds at nearly all their outcrops, being 
one of the most persistent, as well as most characteristic fossils of these layers. 
Still, there are so many varieties of it that it is often difiicult to refer it without 
some hesitation, to its original place. Very many of these varieties have been 
described as distinct species, and others as varieties under varietal names, until 
