﻿BRITISH FOSSIL CEPHALOPODA. 171 



being in the side. The body-chamber is at least half as long again as the diameter 

 at its base, and the aperture is parallel to the lines of growth. The septa are ^ the 

 diameter apart. The sutures rise to the concave side, and tend to become sigmoid. 

 In this species the considerable curvature, the moderate rate of increase, and the 

 closeness of the septa are characters which are not very much interfered with by 

 contortion, but the section seems capable of taking any shape, and hence the variety 

 of names. 



Relations. — The Phragmoceras Brateri of Minister (' Beitrage,' tab. 1, fig. 10, 

 p. 105) has its curvature in the plane of the short diameter, and has a longer 

 body-chamber. Moreover it is a Devonian species. The Phragmoceras arcuatum 

 of Sowerby (' Silurian System,' pi. 10, fig. la, p. 621) seems to be really a 

 Phragmoceras, and there is no sign of the poor specimen referred to it by 

 Portlock having a contracted aperture. The present species differs from Cyrto- 

 ceras subarcuatum, which occurs in the same rocks, by its greater curvature, 

 slower increase, and more oblique septa. 



Distribution.— The whole of those examined have come from the shales of the 

 Bala period at Desertcreat (6). A contorted specimen from the Bala Limestone of 

 Sholeshook may belong to it. 



It is recorded also by Salter from the same horizon, south of Llangollen. 



Cyrtoceras llandoveri, Blake, PI. XXI. figs. 1, la. 



Type.- — Section oval ; the long axis being in the plane of curvature. The mean 

 radius of external curvature is 17 inches when the mean diameter is 3 inches, but 

 the curvature is not very regular. The long diameter increases at the rate of 

 1 in 4. No surface or body-chamber is seen, all being the cast of the septate 

 portion. The surface of the septa is hot seen. They are distant ^ of the long 

 diameter. The sutures are slightly concave towards the inner edge, but towards 

 the outer side they bend backwards and become convex. The siphuncle is a 

 remarkable one ; its centre is situated at ^ the long diameter from the outer edge, 

 and has itself a diameter equal to -^ the same ; it narrows instead of expanding 

 between the septa, and its surface is marked by a number of longitudinal impressed 

 folds; on the upper part of the inner edge there is a conical hollow in the cast 

 indicating some prominence in the shell. The greatest length is 5 inches, and the 

 greatest diameter 2| inches. From the Upper Llandovery rocks at Craig-yr-Wyddon. 

 In the Woodwardian Museum. 



General Description. — Although I have seen specimens which might possibly be 



referred by their general dimensions to this species, and whose siphuncles are 



unseen, yet, as the great character is the form of that organ, the example must at 



present be considered unique. 



z 2 



