﻿136 BRITISH FOSSIL CEPHALOPODA. 



in the intervals between the others, having raised boundaries, and of elliptic shape, 

 with the long axis transverse. The septa are more or less oblique up to 30°, sloping 

 back to the more convex side ; they are distant at first -§-, but at last -^ the 

 diameter ; the convexity is about ^ the diameter. The siphuncle is -| the same, and 

 is situated f across the minor axis, sometimes nearer the convex and sometimes nearer 

 the concave side. The greatest length is 10^ inches, and the greatest diameter 

 nearly 2 inches. The species is found both in stage D and in the band E2 of 

 stage E of the Silurian of Bohemia. 



General Description. — The peculiar ornaments of this species are very closely 

 reproduced in the specimen figured, which agrees with Barrande's species in other 

 respects also ; other examples, which show only the curious lamellar transverse lines, 

 are assumed to belong to the same, though the pitting of the surface is not noticed 

 in all. The section is usually flattened, but in one example it is truly circular. The 

 rate of increase in the figured example is 1 in 10, but this character must be very 

 variable, actual measures on compressed specimens giving from 1 in 5 to 1 in 24. 

 No body-chamber or aperture has certainly been seen. In the figured example 

 there are a number of oval depressions with the longer axis transverse and twice 

 the shorter, the latter being ^V of a line ; their boundaries are raised, and tend to 

 run into irregular longitudinal lines, but the transverse lines are obscure. In other 

 examples the lamelke, broken off upwards in a jagged line, are conspicuous, and there 

 are signs of longitudinal lines. The septa are 7° oblique, curving forward by com- 

 pression, and are ^ the longer diameter apart. The septal surface and the siphuncle 

 have not been seen. The greatest length seen is 4^ inches, and the usual diameter 

 a little more than an inch ; but one example perhaps belonging to this has a longer 

 diameter of 4^ inches. This, however, may be a peculiar form of 0. fimbriatum. 



Relations.— -The peculiar pitting of this figured example, and the remarkable 

 zigzag lamellas of the others, mark off the species very distinctly ; but 0. mocktreense 

 is not far removed. In one example of that species a peculiar network is observed, 

 which may, indeed, be due to Polyzoa, but in any case the longer axes are longi- 

 tudinal. The tapering and the siphuncle, and the regularity of the lines of 

 growth, would also differentiate it. The pitting is too fine and too well marked 

 for ordinary examples to be thought to be 0. fimbriatum with the lamellse run 

 together, but the old example might possibly be so considered. 



Distribution. — In the Lower Ludlow of Leintwardine (2), and in the Aymestry 

 Limestone of Mocktree (1) ; also in the Lower Silurian of Portraine (1) ; the large 

 and doubtful example from the Lower Llandovery Beds of Thrave in the Grirvan 

 district. 



