BRACHIOPODA. 
207 
form a deep, broad, transversely striated pedicle-cavity. The thickened lateral 
margins of this impression are continued anteriorly to about the center of the 
shell, forming an elongate-quadrate diductor scar which encloses a small oval 
adductor. 
The brachial valve has a convex umbo, showing no evidence of concavity in 
early stages of growth. Beneath the beak is a very fine, vertical, linear cardi¬ 
nal process which appears to be continuous with an obscure median longitudinal 
ridge, traversing about one-half the length of the valve. Both of these are 
frequently involved in the shell-substance and evident only in sections of the 
shell. The hinge-plate is deeply divided medially, each lateral portion being 
supported by a deep vertical septum resting on the bottom of the valve. The 
upper surfaces of the hinge processes are obliquely concave the outer and 
anterior angle being much elevated and the slope thence to the dental sockets 
abrupt. The crura are attached to the inner margins of these plates, are not 
curved, but their distal extremities are expanded into spoon-shaped processes 
which have their concave surfaces toward the brachial valve. Their are no 
thickened muscular scars as in the opposite valve. 
The surface is covered with sharply angular, simple plications, most of which 
begin in the umbonal regions, and the broad fold and sinus may bear as many 
as from eight to twelve of these. All the plications are crossed by fine, sharp 
concentric lines of ornamentation, which crenulate the summits of the ridges. 
Shell-substance fibrous, impunctate. 
Type, Rhynchospira nobilis, Hall. Hamilton group. 
Observations. The peculiar structure of this shell involved the earlier de¬ 
termination of its generic relations in much doubt. It was described in the 
Thirteenth Report of the State Cabinet of Natural History (p. 83, 1860), as 
Rhynchospira nobilis^ and in Volume IV of the Palaeontology of New York (p. 412, 
1867), it was referred to Trematospira ? The acquisition of new material"^ 
from the Hamilton group at Thedford, Canada, has afforded the means of de¬ 
monstrating that the shell is not spire-bearing. The external aspect of the 
* Largely by the favor of Professor Samuel Calvin, of Iowa City, Iowa. 
