224 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Genotype.—Pachyglossa dorsiconvexa Cooper, new species. 
Discussion—This genus is suggestive of Lingulella but differs in profile and 
in the character of the posterior margin of the brachial valve. Pachyglossa is 
usually strongly biconvex whereas Lingulella is generally flatly biconvex. The 
interiors of the pedicle valves of both genera are similar but the posterior mar- 
gins of the brachial valves are different. In Lingulella the posterior of the 
brachial valve is occupied by a concentrically marked concave plate. In Pachy- 
glossa, on the other hand, the posterior margin is unmodified and there is no 
concave plate. The margin may be more or less thickened, but that is the only 
modification detected. Other species assigned to this genus are P. biconvexa of 
the Bromide of Oklahoma and P. pachydermata from the Effna formation of 
Virginia. 
PACHYGLOSSA BICONVEXA Cooper, new species 
Plate 7, A, figures 1-12 
Shell of about medium size for the genus, strongly biconvex in lateral profile, 
elongate-oval in outline with the shell substance thick. Lateral margins broadly 
curved with the greatest width slightly anterior to the middle. Anterior margin 
somewhat narrowly rounded. Beak angle about 100°. Surface marked by fine 
and strong concentric growth undulations. 
Pedicle valve having the lateral profile unevenly convex with maximum con- 
vexity slightly posterior to the middle; anterior profile somewhat narrowly 
rounded, the elevation equal in height to about one-quarter the width. Beak not 
conspicuous but meeting the margin. Umbonal region slightly swollen, the swell- 
ing continuing to a point slightly anterior to the middle. Posterolateral slopes 
steep but anterior slope long and only moderately steep. 
Brachial valve having profiles similar to those of the pedicle valve but more 
convex. Posterior margin broadly rounded and only slightly narrower than 
the anterior margin. Umbonal region narrowly convex and the median portion 
of the valve conspicuously swollen and with slopes similar to those of the pedicle 
valve. 
Measurements in mm.— 
Length Width Thickness 
Paratype (pedicle valve 109269a) .......... Ti 11.8 28 
+ (brachial valve 109260b) ......... 13.7 10.6 2.9 
ia Te BOOZ 7 TY aot ois as 15.9 II.4 2.8? 
Types——Holotype: 109271g; figured paratypes: 109269a, 109271f,j,m; un- 
figured paratypes: 109269b, 109271a-e,h,i,k,]. 
Horizon and locality—Bromide formation (Pooleville member-O-oplecia 
gouldi zone) in Oklahoma: At Rock Crossing over Hickory Creek, about cen- 
ter sec. 35, 1.5 S., R. 1 E., Criner Hills, Carter County ; on a branch of Hickory 
Creek in NW34 sec. 26, T. 5 S., R. 1 E., Criner Hills west of Overbrook, Criner 
Hills, Carter County. 
Discussion—This species is characterized by the nearly equal and strong con- 
vexity of both valves in the median region. In this respect it differs from P. ? 
