PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 503 
Discussion.—This genus is characterized by its generally dalmanellid form but 
is distinguished from all members of that group by its impunctate shell. The 
genus is further characterized by the narrow notothyrial chamber enclosed by the 
supporting plates of the brachiophores. This latter structure is similar to that 
of Mimella and the Plectorthidae but differs in having the brachiophore sup- 
porting plates more erect and uniting with the median ridge at its posterior end. 
The genus is most closely related to Corineorthis Stubblefield described from the 
Ordovician of Cornwall, England. It differs from the British genus in its strongly 
biconvex valves. Corineorthis is characterized by having a concave pedicle valve. 
A feature of considerable interest in this genus is the form of the brachio- 
phores. These are divisible into two parts: a base and a “crus.” The base is a 
short, thick plate supported by the brachiophore plates that unite with the 
median ridge. The “crus” is a short, delicate, and sharp point extending from 
the free end of the brachiophore. 
SCAPHORTHIS KAYI Cooper, new species 
Plate 55, D, figures 30-41 
Corineorthis sp. Cooper and Cooper, Bull. Geol. Soc. Amer., vol. 57, p. 113, pl. 3, fig. 13, 1946. 
Shell fairly large, subcircular in outline with the width slightly greater than the 
length. Hinge slightly narrower than the greatest shell width which is located 
at about the middle. Lateral and anterior margins broadly rounded. Surface 
multicostellate, costellae appearing in 5 generations. Costellae of first 4 genera- 
tions of about equal size at the front but those of the fifth generation more slender 
than the rest. About 11 costellae in 5 mm. at the front margin of a valve 17 mm. 
long. 
Pedicle valve moderately and unevenly convex in lateral profile with the maxi- 
mum convexity located in the posterior half. Anterior profile a somewhat nar- 
rowly convex arch with steep sides. Beak forming an angle of about 140°, 
strongly incurved, elevated. Umbonal region convex and median portion of valve 
swollen; lateral slopes steep. Anterior slopes less steep than the lateral ones. 
Interarea long, strongly curved, nearly orthocline. 
Brachial valve gently convex in lateral profile with the maximum convexity 
at about the middle; broadly and gently convex in anterior profile but with a 
pronounced flattening of the median part of the profile. Umbonal region slightly 
sulcate with the sulcus extending anterior to the front margin where it is very 
faint. Sulcus shallow and broad. Flanks narrow, slightly convex with gentle 
lateral slopes but with steeper slopes to the cardinal extremities. Interarea very 
short, anacline. 
Pedicle interior with short, thick dental plates defining a narrow but deep 
delthyrial chamber. Muscle field elongate oval in outline, individual muscles 
difficult to differentiate. Vascula media short, subparallel; ovarian impressions 
small. 
Brachial interior with brachiophore plates uniting with the median septum 
