824 Report or THE State GEOLOGIST. 
Protorhyncha, Hall. 1893. 
(Plate 42, figs. 4-6.) 
Shells biconvex, with a low, ill-defined fold and sinus on 
brachial and pedicle-valves respectively. Pedicle-valve with a 
false cardinal area defined by ridges diverging from the beak. 
Pedicle-passage triangular, rarely showing any trace of deltidial 
plates. Teeth very small, supported by thin lamelle which rest 
upon the bottom of the valve and are not adnascent to the 
lateral walls of the shell. In the brachial valve the dental 
sockets are small; the hinge-plate consists of two minute dis- 
crete processes, the surfaces of which are slightly inclined toward 
each other. These were the bases of the brachial supports 
but show no points of attachment to the crura; they are 
separated by a triangular incision extending to the bottom of the 
valve. There is no cardinal process nor median septum in the 
brachial valve, and no trace of muscular scars in either valve. 
Type, Protorhyncha dubia, Hall. Chazy limestone. 
Distribution. Lower Silurian. 
Orthorhynchula, Hall. 1893. 
(Plate 42, figs. 7-10.) 
Shells rhynchonelloid in contour; hinge-line short, straight, 
extending for about one-third the transverse diameter of the 
valves. A true cardinal area is present on both valves, that of the 
pedicle-valve being considerably the broader, erect, often incurved. 
Each valve also possesses a distinct triangular delthyrium, that of 
the pedicle-valve, according to the evidence at hand, never being 
in any degree closed by deltidial plates. External surface 
strongly and simply plicated, the median fold and sinus being 
well developed. On the interior, the pedicle-valve possesses 
blunt teeth which rest upon the laterally thickened walls of the 
valve and are not supported by lamellz. Between, and slightly 
in front of these lies a short, subquadrate muscular scar. The 
brachial valve possesses a linear cardinal process, on either side 
of which are two discrete crural plates, sharply concave on the 
upper surface and diverging anteriorly for a considerable 
distance. 
Shell-substance fibrous, impunctate. 
Type, Orthorhynchula Linneyi, Nettelroth (sp.). 
Distribution. Lower Silurian (Hudson River group). 
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