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 Stricklandinia ? 

 Balcletchiensis,f a rather large rhynchonelliform shell with a short spondylium 

 in the pedicle-valve, and without cardinal area. 



PARASTROPHIA, gen. nov. 



PLATE LXin. 



Among the species which have been currently referred to Camarella are the 

 well-known Atrypa hemiplicata. Hall, of the Trenton fauna, and the Pentamerus 

 reversiis,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 surface 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 viardinal margin is 

 moderately long and nearly straight, but there is no evidence of a cardinal area 

 on either valve. 



» Tenth Ann. Rept. Director U. 8. Geolo^cal Survey, p. 614, pi. Ixxii, figs. 4 a-d. 1890. 



t See Davidso.v, Silurian Brachiopoda, Suppl., p. 166, pi. ix, figs. 27-29. 



\ The latter has also been lefen-ed by difteient writers to Anastrophia and Tkiplbcia. 



