BRACHIOPODA. 
181 
Observations. These characters, it will at once be remarked, are rhyncho- 
nelloid, but are essentially primitive in all respects. The type of structure, if 
strictly interpreted, does not appear to have been a prolific one. The 
associates of Atrypa dubia in the Chazy fauna, namely, A. plena, Hall, and A. 
altilis. Hall, are larger, more coarsely plicated shells, with a short median sep¬ 
tum in the brachial valve, and a stronger development of the crural bases. 
They evince a higher development of rhynchonelloid characters and perhaps 
may be regarded with more propriety as early representatives of the large 
division here termed Camarotcechia, than as congeneric with Protorhyncha dubia. 
The Poramboniies Ottawaensis, of Billings, from the Black River limestone 
of the Banquette Rapids, appears to be a representative of this structure. 
The relations of Protorhyncha with the genus Orthis are evinced in the 
tendency to the formation of a cardinal area, the usually open delthyrium at 
maturity, and in the short, blunt hinge-processes. 
Genus 0 RT H 0 R H YN C H U L A , GEN. NOV. 
PLATE LVI. 
1889. Orthis, Nettelboth. Kentucky Fossil Shells, p. 41, jil. xxxiv, figs. 7-13. 
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 delthy¬ 
rium, 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 lamellse. 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, Orthis Linneyi, Nettelroth. Hudson River group. 
