PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 933 
STROPHOMENA CONRADI Hall and Clarke 
Strophomena conradi HAtt and CrarKe, Pal. New York, vol. 8, pt. 1, p. 344, pl. 9, A, fig. 3, 
1892. 
Horizon and locality.—Jacksonburg formation in New Jersey: At Jackson- 
burg. 
STROPHOMENA COSTELLATA Cooper, new species 
Plate 255, A, figures I-19 
Shell of about average size for the genus, wider than long; hinge forming 
widest part; cardinal extremities subalate, deflected toward the brachial valve. 
Lateral margins nearly straight or slightly oblique ; front margin broadly rounded. 
Surface marked by fine costellae which are of nearly equal size at the posterior, 
but between each pair of the primary costellae another finer one is intercalated 
for about 4 generations. Costellae increasing in size anteriorly, the primary set 
maintaining its advantage and appearing as the larger of the costellae at the front 
margin and the other costellae being nearly equal in size. Costellae along the front 
margin with less difference in size than the posterior and midregions. At front 
margin of a specimen 20 mm. long 15 costellae of nearly equal size occupy a 
space of 5 mm. 
Pedicle valve with but a slight swelling in the umbonal region, nearly flat at 
about the middle where the valve is geniculated in the direction of the pedicle 
valve. Cardinal extremities deflected toward the brachial valve more or less 
strongly. Median region gently concave and this concavity is extended to the 
region of the cardinal extremities where the valve is slightly swollen. Interarea 
strongly apsacline, moderately long; delthyrium narrow, pseudodeltidium only 
moderately convex. Foramen minute. 
Brachial valve moderately convex in lateral profile with the umbonal region 
flattened ; high point of convexity at about the middle. Cardinal extremities set 
off by moderately deep grooves. Lateral and anterior slopes moderate. Umbonal 
region marked by a shallow sulcus visible for 5 to 8 mm. after which it fades into 
the general surface. Portions of valve bounding sulcus somewhat flattened. 
Interior of pedicle valve: Teeth strong, moderately long ; muscle area varying 
from subcircular to oval and in general having a length slightly greater than the 
width. Muscle field surrounded laterally by low ridge. Diductor-adjustor im- 
pressions subflabellate, separated by a low ridge. Adductor impressions located 
slightly posterior to the middle of the muscle field, slightly elevated on a low 
ridge. Subperipheral rim low, not greatly thickened. 
Interior of brachial valve with short but slender brachiophores almost com- 
pletely buried in secondary shell substance that forms the sockets. Median ridge 
low, extending to about one-third the distance to the front margin. Lobes of 
cardinal process small. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
FT OIOE YEU 5 iys\ clays ale isic.c osaieie re e\s 22.3 21.1 27.4 30.1 4.5 
Paratype (117714b).......... 21.4 20.2 25.1 26.7 4.0 
CUZ ZEAE) sieite testers 17.1 15.9 20.8 22.8 2.8 
