﻿182 BRITISH FOSSIL CEPHALOPODA. 



septum. The diameter across the shell is about 3 h inches, and the greatest diameter 

 of the whorl is 1^ inches. From the Lower Ludlow of Ledbury. In the collection 

 of Dr. G-rindrod. 



General Description. — The roughness of the ornaments and forward curve of the 

 septa, which in the absence of the remarkable siphuncle distinguish this species, are 

 not commonly met with, there being only two other specimens I can refer here. 

 One shows the same kind of ribbing dying off toward the outside and also towards 

 the aperture, which, like the ornaments, is forward inside and curves backwards 

 sigmoidally towards the outside. On this the radial epidermids, distant 18 per line, 

 are well exposed. The other is one of the examples figured by Sowerby as Phrag- 

 moceras nautilaceum. The second, or more involute example figured by that author, 

 must be taken as the type to retain the specific name. This one is but a broken 

 fragment, which, however, may well be referred here by its rough ornaments and 

 its septa. 



Relations. — If this be a Cyrtoceras, there is very little doubt of its distinctness 

 from all others ; none of those showing so much curvature being anything like it. 

 On the other hand, if it be a Trochoceras, its peculiar siphuncle, combined with the 

 irregularity of its ribbing, separate it well from all those in which those characters 

 are known. 



Distribution. — In the Lower Ludlow of Ledbury (2), and in some Upper Silurian 

 rock at Dudley (1). 



Section Mediogastrica. 

 Cyrtoceras subarcuatum, Portlock, PI. XX. fig. 7. 



1843. Orthoceras subarcuatum, Portlock, ' Geol. Eeport,' pi. 28, fig. 9, p. 374. 

 1865. Cyrtoceras subarcuatum, Salter, ' Catalogue of Fossils in the Museum of Practical 

 Geology,' p. 32. 

 Syn. 1843. Orthoceras breviconicum, Portlock, loc cit., pi. 28, fig. 8, p. 373. 



Type. — Section oval, with the curvature in the long diameter, and the narrower 

 end of the oval on the convex side. The diameters are in the ratio of 21 to 13. 

 The long diameter increases at the rate of 1 in 2. The inside edge is almost straight, 

 and the outside edge is only slightly curved. The surface had only transverse lines 

 of growth, nearly parallel to the septa, but increasing in strength and becoming 

 oblique on the concave side. The body-chamber continues for 10 lines on the 

 convex side without change. The septa have a very slight convexity ; their distance 

 increases more than proportionally towards the body-chamber, from -^ to y 1 ^ the 

 corresponding long diameter. The sutures are slightly undulating, the convexity 

 being on the inner side ; the direction is at right angles to the inner edge of the 



