﻿BRITISH FOSSIL CEPHALOPODA. 199 



diameter, and are at variable distances from i to -^ the same ; in a specimen of 

 circular section the distance is \. The siphuncle is situated from i to \ of the 

 diameter from the ventral edge, and consists of slightly inflated bulbs. Length, 

 3 inches ; diameter, 1^ inches. From stage E, or Upper Silurian. 



General Description. — There is not an absolute agreement between our forms 

 and the Bohemian, but the differences appear to be within the range of what may 

 be called varietal. The section is circular, but there is rather more convexity on 

 the ventral side. The rate of increase on the septal portion is at the rate of 1 in 3. 

 The body-chamber is somewhat conical, and has a length of from f- to -| the greatest 

 diameter in different examples. The aperture consists of a transversely elliptic 

 dorsal opening, and a ventral opening and passage united, or slightly marked off, of 

 the same diameter as the dorsal opening ; the apex of the shell lies between the two 

 parts of the aperture, which occupies ^ of the largest diameter, and is scarcely 

 marked off by any constriction. The septa have # convexity of rather more than ^ 

 the diameter, and are distant \ of the same ; the siphuncle is situated near the 

 ventral border, and is bulbous. Greatest diameter, \\ inches. An example figured 

 (PI. XXIII. fig. 7) shows rather a remarkable feature on the body-chamber. This is 

 a pair of depressions radiating from the interval between the two parts of the aper- 

 ture, but not joining the latter. They are long and narrow, but one is longer than 

 the other ; what may be their significance I cannot at present even guess. 



Relations. — The typical Bohemian forms, with transversely elliptic section and 

 siphuncle not lateral, approach by these characters and the form of the aperture 

 very close to G. ellipticum ; but the more inflated and rounded form of the latter 

 seems sufficiently to distinguish them. Our English forms are certainly distinct 

 and are more nearly allied to G. crater, which has, however, much greater septal 

 convexity, and the aperture, though similar, is by no means identical. 



Distribution. — In the Lower Ludlow of Ledbury (3, and 2 doubtful), and in the 

 Wenlock Limestone of the same locality (1 doubtful). 



Genus Phragmoceras. 



Phragmoceras prius, Blake, PI. XXIY. fig. 5. 



Type. — The section is elliptic, with the long axis in the plane of curvature. The 

 ratio of the axes about 3 to 2. The mean radius of curvature 1h inches when the 

 mean diameter is li inches. The rate of increase is 1 in 8, and this is continued on 

 the body-chamber till the commencement of the aperture. In the transverse 

 direction the body-chamber rapidly increases to the middle and then decreases 

 again, so as to be bulging or oval. The dorsal aperture is elliptic, with the long 

 axis in the plane of symmetry, and of small dimensions ; the rest is not clearly 



