﻿BEITISH FOSSIL CEPHALOPODA. 123 



rate riblets, or crinkly lamellae, continuing in a uniform curve which is direct on one 

 of the broader and both of the narrower sides, but undulates backwards on the 

 other broad side. These are at varying distances, being 7 per line at a larger 

 diameter, and only 5 at a smaller. The body-chamber contracts a little towards the 

 aperture, which is simple and transverse. The septa are direct and distant f- the 

 diameter ; their convexity is moderate. The siphuncle is not properly seen. The 

 greatest length is 12 inches, and the greatest diameter 2 inches. From the Lower 

 Ludlow of Ledbury, in the collection of Dr. Grindrod, after whom it is named. 



General Description. — Other examples in the same collection confirm the general 

 tapering and ornaments. One of these, a polished section, gives the details of the 

 septa. They are direct and distant \ the rather flattened diameter, and their 

 convexity is not more than -|- the same. The siphuncle is central in the diameter 

 exposed, but by pressure it is displaced in other diameters. It has a diameter 

 between the septa of \ the whole, its elements being thus cylindrical. There is 

 a little organic deposit at the necks, and it is impossible to distinguish the sub- 

 stance of the covering of the siphuncle from that of the septa. In the sides of 

 the earlier chambers there are very instructive instances of organic deposit. 



Relations. — This magnificent form is obviously a near ally of O.jimbriatum. It 

 is not, however, fluted or coloured longitudinally, and the transverse lines are in 

 much finer festoons, so as to be merely minutely undulating. They are, however, of 

 the same type as in 0. Jimbriatum, and justify the separation of the latter from 

 0. annulatum. 



Distributions — In the Lower Ludlow of Ledbury (3), and possibly in the Upper 

 Ludlow of Ludlow (1). 



Orthoceras pomeroense, Portlock, PI. XI. fig. 1. 



1843. Orthoceras pomeroense, Portlock, ' Geol. Eeport,' pi. 26, fig. 4. 



Syn. 1843. Orthoceras irregulare, Portlock, loc. cit., p. 375. (Not of Minister.) 

 1843. „ complanatoseptum, Portlock, loc. cit., pi. 28 B, fig. 1, p. 374. 



1843. „ tumidum, Portlock, loc. cit., pi. 28, figs. 5, 6, p. 373. 



Query 1843. Orthoceras regulare, Portlock, loc. cit., p. 376, pi. 27, fig. 46. (Not of Minister.) 



Type. — The specimen to which Portlock's name, here adopted, was assigned, 

 consists merely of fragments of shell surface, showing sharp transverse irregular 

 lines of growth corresponding to a tolerably large species. It is, however, the 

 least objectionable of the names quoted above, which together are thought to 

 represent a fairly well characterised species. The type is from the Bala Series of 

 Desertcreat, and is in the Museum of Practical Geology. 



General Description. — The section is always seen elliptic, and perhaps was natu- 

 rally so, as it retains that shape when the pressure has been perpendicular to the 

 axis. The rate of increase is with difficulty ascertainable, but is probably between 



r 2 



