﻿BRITISH FOSSIL CEPHALOPODA. 187 



General Description. — No examples show the outline better than the type, all of 

 them being contorted. Nor is the curvature on both sides so equal in others, but 

 both the specimen referred by Portlock to Gomphoceras subfusiforme and the figured 

 example show a gradual contraction to an apparently simple aperture, the body- 

 chamber being about equal in length to the septal portion. In the latter there 

 appears to be considerable convexity of septa, and there is a well-marked external 

 siphuncle on the more convex side. 



Relations. — This, with P. intortum, first introduces the Inflati into the British 

 rocks ; and the latter, besides the peculiarity at its aperture, which may be abnormal, 

 is a stouter shell in comparison to its length. 



Distribution. — In the Bala Beds of Desertcreat (2), Pomeroy (1), and Twllddu, 

 Carnarvon (1). 



Poterioceras (?) intortum, Blake, PI. XXIY. fig. 4. 

 Syn ? 1843. Gomphoceras subpyeiforme, Portlock, ' Geol. Eeport,' pi. 28a, fig. 1 (not of Miinster). 



Type. — Section oval, the long diameter in the plane of symmetry, and the greatest 

 breadth •§ along the diameter nearest the more convex side. Ratio of diameters, 

 19 to 15. The general shape is irregular, with a very slight general curvature. 

 The rate of increase on the septal portion is about 1 in 2, the greatest diameter 

 being at the last septum, from whence on the body-chamber a decrease takes place 

 towards the aperture. The sides are nearly straight, tapering at the rate of 1 in 3, 

 but the dorsal border is more regularly convex than the ventral. The shell thickens 

 near the aperture, but at last a sudden inbending takes place to an opening much 

 smaller than the general section. This may, of course, be an abnormal feature. The 

 shell is of considerable thickness, and has feeble, rather regular transverse lines of 

 growth. The septa have a very slight convexity, and are -^ the mean diameter 

 apart. The sutures are nearly direct, but slightly undulating on the side. The 

 siphuncle is not certainly seen, but appears to be nearly external on the more 

 convex side. Greatest length, 2^ inches ; greatest diameter, 19 lines. From Bala 

 Beds at Piedmont, Ayrshire. In the Museum of Practical Geology. 



General Description. — The fossil figured by Portlock, and referred by him to 

 G. subpyriforme of Miinster, may belong to this species, but it is flattened out, and 

 its true section cannot therefore be known ; moreover its aperture is wanting, 

 and the position of its siphuncle is unknown. Thus the remarkable inbending 

 at the aperture, as seen in the type, remains unconfirmed. 



Relations. — The greater width in comparison to the size, when both are equally 

 flattened, separate the two Portlockian fossils, and also the better preserved forms to 

 which they are severally referred. The Gomphoceras primum of Barrande bears a 



2 b 2 



