﻿206 BRITISH FOSSIL CEPHALOPODA. 



by compression, -^ of the same ; the last one in some half the usual size. The 

 siphuncle is internal and bulbous ; the bulbs are elliptic ; the long diameter in the 

 plane of curvature reaching to -|- the whole diameter. The greatest diameter is 

 4 inches. 



Relations. — Although the only indication of the aperture given by Sowerby is 

 that the " beak " is " direct," which it certainly is in the specimens seen, the 

 coincidences in other respects will be. seen to be too remarkable to leave much doubt 

 that we have here the true P. arcuatum. It differs from P. ventricosum in its 

 greater curvature ; in the prominence and shape of its larger aperture ; in the 

 character of the ornaments, and perhaps in the crenulation of the base of the body- 

 chamber ; in its straighter and more distant septa. The specimen figured by 

 Sowerby (fig. 5), as belonging to his P. ventricosum, shows the produced aperture 

 and the irregularity of the ribbing, and so belongs here. From P. imbricatum this 

 species differs in the character of its ornaments and its general shape. Barrande 

 has compared P. arcuatum with Cyrtoceras Murchisoni ; but if my interpretation be 

 right, the latter can have no relation to it unless it be a Phragmoceras. The real 

 Bohemian representative is P. comes, of a little later date. It has not been so 

 compressed as ours ; but with a little squeezing there would be nothing to 

 choose between them, but P. comes shows no crenulations at the base of the body- 

 chamber. 



Distribution. — In the Wenlock Limestone of Dudley (3) ; in the Lower Ludlow 

 of Ledbury (8) and of Mocktree (1). 



Phragmoceras externum, Blake, PI. XXVI. fig. 3. 



Type. — Section rather roundly triangular than circular ; axes unequal, the 

 shorter axis being in the plane of curvature in the ratio of 14 to 15. The angle of 

 the triangle towards the outside curvature slight. The rate of increase on the septate 

 portion is a little less than 1 in 2. The shell begins to contract before the last 

 chambers, but the aperture is lost ; no ornaments are seen. The septa are very 

 nearly flat, and are distant \ the mean diameter. The sutures slope a little back- 

 wards towards the convex side. The siphuncle is external, situated in the angle of 

 the triangular section, and has a sub-elliptic shape. Greatest length, 2|, inches ; 

 greatest diameter, 1\ inches. From the Lower Ludlow of Ledbury. In the collec- 

 tion of Dr. Grindrod. 



General Description. — The type is unique. 



Relations. — The contraction of the body-chamber renders it highly probable 

 that this is a Phragmoceras and not a Cyrtoceras, allied by its external siphuncle to 

 P. devonicans, Barrande ; but that is altogether too large a shell : no Cyrtoceras is 

 near enough to it for comparison. 



Distribution. — In the Lower Ludlow of Ledbury (1). 



