614 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
on each valve. The sides are compressed in both genera, and the shells are nar- 
rowed posteriorly but much more so in the American genus. Cowper-Reed de- 
scribes the exterior of Metacamarella as “externally punctate.” All available 
evidence indicates that the exterior of Parallelelasma is smooth. 
Through the kindness of Dr. Helen M. Muir-Wood of the British Museum, 
who has examined the types of Metacamarella preserved in the British Museum, 
it is possible now to say that the Scottish genus is not punctate on the exterior. 
Dr. Muir-Wood says “Most of the specimens are much decorticated and the 
shell tends to weather in overlap scales but these do not appear punctate. The 
shell is very finely fibrous, the fibres running obliquely to the surface in the outer 
layers, and the broken off ends of the fibres do give the shell a somewhat granu- 
lar appearance which may be taken for punctation.” 
St. Joseph (1941, p. 399) does not mention presence of exopunctae in his 
discussion of the genus. The five sections of the brachial valve illustrated show 
well the subparallel plates of the brachial valve, and low ridges between these 
plates suggest that the muscles were confined between these plates as in Paral- 
lelasma. Unfortunately, no illustration of the “crura” is given. 
Metacamarella has short, subparallel plates like those of Parallelelasma in the 
brachial valve, but the cardinalia are described as having long, stout crura, re- 
curved and diverging at about 60°, close to the hinge line. This is quite unlike 
the short, straight brachial processes of the Alabama genus. It is concluded there- 
fore that Metacamarella, although superficially like Parallelelasma, is a distinct 
genus but probably belongs in the family Parallelelasmatidae. 
PARALLELELASMA PENTAGONUM Cooper, new species 
Plate 115, H, figure 49; plate 118, B, figures 11-19; plate 119, F, figures 17-31; 
plate 121, A, figure 1 
Shell thin, elongate, pentagonal in outline with a narrow posterior-but a wide 
anterior ; lateral margins obliquely straight for about two-thirds the length; an- 
terolateral extremities angulated ; anterior elongate and broadly rounded. Bicon- 
vex, the brachial valve somewhat deeper than the pedicle valve; anterior com- 
missure rectimarginate to broadly uniplicate. Lateral commissure broadly ser- 
rate anteriorly. Beaks low, somewhat closely appressed. Posterior third smooth, 
anterior two-thirds marked by broad, low, rounded costae. Lateral edge nar- 
rowly angulated and somewhat produced and elevated at its anterior end. 
Pedicle valve gently convex in lateral profile; broadly and gently convex in 
anterior profile ; umbonal region narrowly swollen ; median region gently inflated ; 
margins deflected slightly and separated by a narrow, shallow sulcus; region be- 
tween two sulci forming a broad ill-defined sulcus. 
Brachial valve gently convex in lateral profile, somewhat more convex pos- 
teriorly than in the anterior half; anterior profile broadly and gently convex. 
Umbonal region narrowly swollen ; median region gently inflated. Lateral slopes 
narrowly rounded and precipitous. Costae anteriorly forming an ill-defined fold. 
Interior as defined under the genus. 
