﻿BRITISH FOSSIL CEPHALOPODA. 179 



curve forward on the convex sides. The siphuncle is external and bulbous, the 

 transverse diameters of the bulbs being greater than the longitudinal. The greatest 

 length is 2£ inches, and the greatest diameter 11 lines. From stage E or Upper 

 Silurian. 



General Description. — The section, as seen in an example in the Museum of 

 Practical Geology, is nearly circular ; but its longer diameter is in the plane of 

 curvature. The mean radius of external curvature is 16 lines, the mean long 

 diameter being 10 lines. The rate of increase is 1 in 3£ in a flattened example, and 

 1 in 5 in one uncompressed. The surface is smooth on the sides, but on the concave 

 border are rugosities which pass back over the septa, and consist of upward imbri- 

 cations, thrice as numerous as they. The body-chamber has a length equal to its 

 diameter, and the aperture, as far as seen, appears to be simple. It lies parallel to 

 the septa, and has a slight constriction round it. The septa are very slightly 

 convex and very approximate, being -^ T of the long diameter apart, which becomes 

 -jJg- in a flattened example. The sutures have very slight concavity, and bend forward 

 towards the convex side. The siphuncle is external, and consists of closely-set, well- 

 marked bulbs, whose transverse diameter is greater than the longitudinal. The 

 largest specimen is imperfect at both ends ; the greatest length is 2f inches, and the 

 greatest diameter 2 inches. 



Relations. — This is very closely related in many respects to C. corniculum, but 

 the siphuncle is not cylindrical, as in that species, but very bulbous ; other 

 differences of less certain value are the greater curvature and the greater closeness of 

 its septa. 



Distribution. — In the Lower Ludlow of Ledbury (3). 



Cyrtoceras intermedium, M'Coy, PL XX. fig. 6, PI. XXI. fig. 2, and 



PL XVIII. fig. 13. 



1851. Phragmoceras intermedium, M'C<>y, 'Annals of Nat. Hist.' Ser. II. vol. vii. p. 45. 



1852. „ „ M'Coy, ' British Palaeozoic Fossils,' p. 322. 

 1873. Phragmoceras ? Salter, ' Cambrian and Silurian Fossils,' p. 174. 



Syn. 1838. Phragmoceras arcuatum, Sowerby, ' Silurian Syst.' pi. 11, fig. 1, p. 621. Not var. a 

 of pi. 10, fig. la. 



Type. — Section a rather flattened oval, the larger end towards the convex side, 

 the long axis being in the plane of curvature. The ratio of the axes is as 5 to 3. The 

 curvature is considerable, the mean radius being only -f of the corresponding mean 

 diameter, viz. about If inches. The rate of increase of the long diameter on the 

 septate portion is 1 in 8, and this continues uniformly on the body-chamber, till near 

 the aperture, where the surface appears to bend in as if to come to a complex aper- 

 ture ; but this part is not well preserved, and the appearance is no doubt due solely 



2 a 2 



