﻿202 BRITISH FOSSIL CEPHALOPODA. 



Mocktree (L), and Presteign (1) ; in the Aymestry Limestone of Dudley (5). It is 

 also recorded by G-arner from the Lower Ludlow of Dudley, and by Salter from 

 the same beds at Coalbrookdale. The latter author, in the third volume of the 

 'Memoirs of the Geological Survey,' records it also from Caradoc; but though 

 I have examined all the Palaeozoic Cephalopoda in the Museum of Practical Geo- 

 logy, I have not seen any either so labelled or actually belonging to the species. 

 I think, therefore, there must be some mistake on the point. 



Phragmoceras imbrtcatum, Barrande, PI. XXV. figs. 2, 2a. 

 1865. Phragmoceras imbricatum, Barrande, 'Syst. Silur. de Boheme,' pi. 46, 175, and 244, p. 212. 



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

 diameters are in the ratio of 4 to 3. The curvature is considerable, the mean radius 

 being: 24- inches when the mean diameter is If inches. The rate of increase on the 

 septate portion is 2 in 5, measured along the convexity. Examples have been* 

 found showing the initial cap with a central perforation and concentric stria?. The 

 body-chamber has a length slightly greater than its basal diameter. It continues 

 the convex curve without change, but is rather swollen on the concave side. The 

 aperture consists of a large opening which is transversely elliptic, with axes in the 

 ratio of 7 to 4, — it is somewhat produced outwards as well as forwards ; of a passage 

 which is closed, in parts, and which forms nearly a flat surface between the two 

 openings, not quite parallel to the base of the body-chamber, but rising towards the 

 dorsal side ; and of a small opening which is elliptic, with the long axis ventro- 

 dorsal, and running out into a beak on the ventral side. The shell is thin and 

 consists of lamellae, which imbricate upwards, and cover the surface with delicate 

 lines, which curve rapidly backwards on the sides, meet in a rounded curve on the 

 convex side, and bend also back to meet on the concave side in a backward running 

 tongue which lies in a median furrow. These lines are about -f of a line apart in the 

 middle of the side. There are feeble crenulations at the base of the body-chamber. 

 The septa have a convexity of \ their diameter, and are distant the same proportion. 

 The sutures are nearly direct, and show very little concavity on the sides. The 

 siphuncle is elliptic, bulbous, and internal, about \ the whole diameter in its long 

 axis. Length, 3^ inches; greatest diameter, 2 inches. From stage E, or Upper 

 Silurian. 



General Description.' — The' section of the British specimens, like that of the type, 

 seems to vary independently of compression. It is elliptic, with the long axis in the 

 plane of curvature, the ratio of the diameters varying from 4 to 3 up to 3 to 2, but 

 in some they are more equal than in either of these ratios. The external curvature 



