Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/589

Rh NOTES ON THE CAMBRIDGE GKEENSAND. 503

The species, indeed, is very rare ; and only a few portions of the shell remain on that figured, which measured inch by about 1^ inch. The shell appears to have been moderately thick ; and the ribs stand out in strong relief on the cast.

It somewhat resembles L. Galliennei of D'Orbigny ; but this species is wider, is much more compressed, and is strongly striated over both ribs and interspaces — characters which sufficiently distin- guish it.

BRACHIOPODA.

Rhtnchonella sulcata, Park.

Rhynchonella sulcata, Park, Geol. Trans, ser. 1. vol. v. p. 59 ; Dav. Cret. Brach. pi. x. figs. 18-36.

The varieties of this species are very numerous, all gradations being found between the large and sparsely ribbed shells, and the smaller forms which bear numerous closely set ribs. The specimen noticed in my previous paper as R. comjpressa (really dimicliata) may be only another extreme variety. Mr. Davidson, to whom it has since been sent, remarks that it is much more transverse than any R. sulcata which has come under his notice, and that it is very like some forms of R. dimicliata ; but for all that he would not be surprised if it were only a compressed and abnormal form of R. sulcata, so difficult is it to state positively to which species a single and isolated individual belongs.

Those shells previously known as R. latissima are now considered to be R. dimicliata, var. convexa ; but the Cambridge specimens may after all be only an extreme variation of R. sulcata.

ACTINOZOA.

Trochocyathus angtjlattjs, Duncan, sp.

Smilotrochus angulatus, Duncan, Suppl. Cret. Corals, pi. vii. figs. 7 and 8.

In 1867 Prof. Duncan described as new forms two species of corals from the Cambridge Greensand, referring them to the genus Smilotrochus ; one of these, S. elongatus, I have previously shown to be really a Trochocyathus, by discovering that it possessed epitheca, exhibited a columella, and was clearly pediculate — that it was, in fact, identical with Trochocyathus conulus of Edw. and Haime.

I had not then any proof that the second species, S. angulatus, belonged to the same genus, though I regarded it as exceedingly likely. Having recently, however, split open many specimens of this coral, I have ascertained that it possesses as distinct a colu- mella as its larger congener, though, of course, shorter in proportion to the squat growth of the species.

Edwards and Haime's description, viz. " columella well deve- loped, composed of prismatic or twisted processes disposed fascicu- larly or in a single row," applies equally to both species.

Q.J.G. S. No. 131. 2l