﻿BRITISH FOSSIL CEPHALOPODA. 201 



curvature of the shell or of the pattern of the aperture. In this species the section is 

 an ellipse, with the long axis in the plane of curvature ; but the ratio of the axes is 

 very variable, from 2 to ] down to 5 to 4. M'Coy, in his description of this species, 

 states that the figures given by authors do not sufficiently indicate the flattening of 

 the septate portion. It appears, however, that his specimen must have been 

 peculiar ; for in most, though not in all, it is the body-chamber that becomes most 

 flattened, and the most nearly circular sections are found on the small ends. The 

 curvature is about that of the type, and does not appear to vary greatly. The 

 body-chamber varies in length from a little less to a little more than its basal long 

 diameter. The aperture is more open in youth, and then consists of a large opening 

 scarcely transverse, a small one of a quarter the linear dimensions, and a narrow 

 passage (fig. 2a) ; later the two openings become more distinct (fig. 3), and, finally, 

 the passage closes up irregularly (fig. 1), and the large opening grows transverse. 

 The surface of the shell, however, is not produced in such as agree in other respects 

 with the type. Hence Sowerby's fig. 5 must be excluded from the species. The 

 ornaments are most marked on the convex side, where they form, in some, strong 

 steps having an upward imbrication. In the body-chamber of some they degenerate 

 into rugas of growth with intermediate lines, but are never quite lost. They curve 

 deeply backwards, and are on the average about 1 line apart. The septal convexity 

 is from \ to \ the long diameter. The distance of the septa in quite a young form 

 reaches as much as f the corresponding diameter, but the true distance is from 

 tV t° T4 iu the middle of the side. They had but little strength, as they are utterly 

 broken down in section. The sutures are essentially sigmoidal. The siphuncle is 

 seen in several to be internal ; it is elliptic in section, the long diameter in the plane 

 of curvature reaching -|- that of the septum. The type is one of the largest 

 specimens known, but some have a diameter at the aperture of over 4 inches. 



Relations. — The form corresponding to this in the Bohemian fauna is the 

 P. Broderipi, which is there as widely spread as our own species is here. The 

 resemblance is close ; their genetic relationship cannot be doubted, but that species 

 appears to be uniformly more curved than ours is ; as to the large aperture being 

 more rounded, I believe our species has not a very transverse opening, those 

 specimens which should prove it either being distorted or belonging to another 

 species. It is doubtful whether a slight increase of curvature ought to be sufficient to 

 distinguish a species, but it is probably hopeless to attempt to suppress P. Broderipi 

 as a name. From the other British Phragmocerata it differs in one case (P. imbri- 

 catuin) by its ornaments, and in the other (P. arcuatum) by its non-produced 

 aperture and closer sigmoidal septa. 



Distribution. — In the Upper Llandovery rocks of May Hill (2 ); in the Wenlock 

 Shale, Llandewi (1) and Ledbury (1); in the Wenlock Limestone of Dudley (4) 

 and of Malvern (4) ; in the Lower Ludlow of Aymestry (2), of Ledbury (4), of 



2 D 



