PARTI CHAZYAN AND RELATED BRACHIOPODS—COOPER 743 
septa; cardinal process covered by a narrow, convex chilidium; bulbous cardi- 
nal process buttressed by a short shaft lying at the posterior termination of 2 
thin, elevated septa which rise to their highest point near the anterior margin; 
anterior ends of septa not thickened; inner margin not thickened; entire inner 
surface marked by coarse granules especially well developed in the anterior parts 
of the shell. 
Genotype—Syndielasma biseptatum Cooper, new species. 
Discussion.—This genus in its external form and profiles is most like Sower- 
byella. It also resembles Sowerbyella in its interior characters but has a num- 
ber of primitive features which separate it from that genus. The known speci- 
mens of Syndielasma are not so concave as usual in Sowerbyella, and the shell 
is much more compressed than is usual in that genus. The pseudodeltidium of 
Syndielasma is much reduced and in this respect has surpassed Sowerbyella. 
The chilidium of Syndielasma is well developed and forms a narrow arch over 
the cardinal process. Thus the posterior characters of Syndielasma, if well pre- 
served, should distinguish it from Sowerbyella. 
The 2 long, high septa of the brachial interior of Syndielasma are obviously 
like those of Sowerbyella. The later members of the latter genus, however, usually 
have the front ends of the septa thickened and grown together by shell substance 
to produce a steep anterior slope off the front ends of septa. The real distinction 
between Syndielasma and Sowerbyella is in the cardinalia, particularly the cardi- 
nal process. In Sowerbyella the cardinal process is joined to the chilidial plates 
and brachiophores to form a tentlike structure that overhangs the notothyrial 
region. In Syndielasma, on the other hand, the cardinal process is a thick boss 
with a short shaft occupying the notothyrial cavity. The brachiophores of 
Syndielasma in their slender and widely divergent character are not unlike those 
of Sowerbyella. Syndielasma thus combines features that are definitely like those 
of Sowerbyella with others that remind one strongly of Palaeostrophomena and 
its allies. 
It is doubtful if Syndielasma is one of the progenitors of Sowerbyella because 
it occurs with Sowerbyella bellarugosa. This species occurs at the same horizon 
and locality and has the tentlike cardinalia of true Sozwerbyella. It is best to 
regard Syndielasma as an early off-shoot from the line that produced Sowerbyella. 
SYNDIELASMA BISEPTATUM Cooper, new species 
Plate 185, C, figures 14-29 
Shell attaining about 4 inch in width, wider than long, semiellipitical in out- 
line; hinge forming the greatest shell width; cardinal extremities alate; sides 
oblique ; anterior margin broadly rounded; shell thin, valves compressed to form 
an unusually narrow body chamber ; costellae narrowly rounded, distant, about 11 
in 5 mm. at the front margin. A few oblique wrinkles along the posterior margins. 
Pedicle valve gently convex in lateral profile; anterior profile broadly and 
slightly convex, the maximum convexity at the middle; beak small, protruding 
slightly posterior to the posterior margin; umbo narrowly and slightly swollen 
