BRACHIOPODA. 
221 
given by Billings and Walcott, and these afford no indication of its generic 
character except that it has a plicated rhynchonelloid exterior. 
Mr. Walcott’s species, C. minor* from the Olenellus zone, at Stissing 
Mountain, Duchess county, N. Y., is a smooth, biconvex species, and the 
figures of internal casts given by this author indicate that the pedicle-valve 
possessed a small spondylium beneath the beak, resting upon the botton of the 
valve, the plates bounding it being produced about and just within the cardinal 
margins. The brachial valve appears to be without a median septum or spon¬ 
dylium, but may have had a narrow hinge-plate. Mr. Walcott states that the 
casts studied by him are imperfect and the generic reference only provisional. 
With Camarella should probably be placed Davidson’s StricJdandinia ? 
Balcletchiensis,f a rather large rhynchonelliform shell with a short spondylium 
in the pedicle-valve, and without cardinal area. 
PARASTROPHIA, gen. nov. 
PLATE LXIII. 
Among the species which have been currently referred to Camarella are the 
well-known Atrypa hemiplicata, Hall, of the Trenton fauna, and the Pentamerus 
reversus,X Billings, of the Anticosti group. These are shells of considerable size. 
The inequality of the valves, which becomes apparent in old shells of Camarella 
Volborthi, is here carried to a greater extreme, becomes developed in immature 
growth-stages, and in the mature individual the brachial valve is much the 
more convex, its umbo and beak projecting conspicuously beyond that of the 
pedicle-valve. These shells have essentially lost their rhynchonelloid expres¬ 
sion, being broad and transversely oval in outline, while the median fold and 
sinus are retained in their normal relations. The surhice bears low, rounded 
plications which are stronger on the fold and sinus, but are also apparent on 
the lateral slopes near the margins of the valves. Over the median and um- 
bonal portions of the valves they are obsolescent. The c.ardinal margin is 
moderately long and nearly straight, but there is no evidence of a cardinal area 
on either valve. 
* Tenth Ann. Kept. Director U. S. Geological Survey, p. 614, pi. Ixxii, tigs. 4a-d. 1890. 
t See Davidson, Silurian Brachiopocla, Suppl., p. 166, pi. ix, tigs. 27-29. 
I The latter has also been i eferred by different writers to Anastrophia and Tkiplecia. 
