On an Orthoceras of the Millstone Grit

Abstract

I have met with an Orthoceras in a bed of black shale, immediately underlying the Cayton-Gill Beds, in the parish of Bishop Thornton, near Ripon, which presents several points of interest, apparently new. It occurs in a very fragmentary condition, associated with Posidonomya Becheri in abundance, some small fishes’ teeth and scales, and a few flag-like vegetable remains. The lower part of the fossil is about an inch and a half in length, consists of a number of meniscus-shaped portions, and tapers to a point, which, is bent slightly to one side. Above this, which in the fossil is solid (Fig. 1, 2, 3 a ), there is a hollow chamber (Fig. 1, 2, 3 b ), the walls of which are very thin, and marked externally with parallel rings from one-sixteenth to one-tenth of an inch apart (Fig. 3 b ). The walls of this chamber I have never yet found in a perfect state: but such portions, as I have met with, appear to show that the chamber expanded regularly until it was about an inch in width. But the most interesting feature is the occurrence of two well-marked semi-oval lobes in two specimens in my possession. These lobes lie one on each side of the lower part of the wide chamber (Fig. 1, 2 c ), and appear to me to be the fossil-marks of fins. There are, however, no other indications of structure than the form, which is well defined in its outline. The lobes also are not flat, but …