﻿220 BRITISH FOSSIL CEPHALOPODA. 



of the diameter. Another has the typical rate of increase, and the last whorl .35 of 

 the diameter. The whorls scarcely touch, owing to the want of symmetry. The 

 section is elliptic, the long diameter in the plane of curvature being 13-f lines when 

 the short is 11 lines. The surface was probably smooth. The septa are 32, or even 

 more, in half a whorl (fig. 3) ; they are nearly straight at first and then bend rapidly 

 forward to the front, and are almost flat transversely. The siphuncle is external 

 and bulbous. 



Relations. — The only other smooth, little elevated Trochoceras in British strata 

 is T. tortuosum, whose section at once distinguishes it. Among the Bohemian forms 

 T. anguis has a less proportionate thickness of ^whorl, and T. priscum, which seems 

 to be the commoner species, has a compressed front. 



Distribution. — In the Wenlock Shale, Ledbury (1) ; in the Wenlock Limestone, 

 Ledbury (1) and Dudley (1); and in the Lower Ludlow of Ledbury (5) and of 

 Mocktree (1). 



Trochoceras gyrans, Blake, PI. XXIX. fig. 4. 



Type. — Eate of increase 1.5, last whorl .28 of the diameter. Thus the whorls 

 are slightly out of contact throughout ; \\ whorls are seen. The elevation is very 

 slight; and the section is slightly quadrate. The ornaments are only backward- 

 curving lines of growth, which are somewhat grouped on the inner side, and 

 especially on the earlier part. No septal characters seen. Diameter 47 lines. From 

 Wenlock Limestone, Eastnor. In the collection of Dr. Grindrod. 



General Description. — Another example in the same collection, also in limestone, 

 shows two whorls, of which the first is certainly unsymmetrical. The dimensions 

 are the same, as are the subquadrate section, a little broader than thick, and the 

 general smoothness. The body-chamber occupies \ a whorl at least. Septa not 

 clearly seen, but their convexity is not slight. With these may be associated a fossil 

 in the Museum of Practical Geology, whose rate of increase is 1.45 and breadth of 

 last whorl is .24 of the whole, the difference being possibly due to the imbedding of 

 the whorl in the stone. The septa are approximate \-\ diameter apart, the sutures 

 undulating; the siphuncle is f the diameter towards the outside and consists of 

 oblique bulbs. There is thus no proved connection between these beyond their 

 proportions being somewhat similar, making both evolute, so that the true septal 

 characters of T. gyrans may be different. 



Relations. — The nearest form to this is T. speciosum, whose whorls are only just 

 in contact, if even they really are, and which has a smooth surface. The present, 

 however, is more evolute, its section is more quadrate, and of course, if the example 

 above described really belongs to it, the septal characters are quite distinct, as 

 indeed the convexity of the septa in any case is. 



Distribution. —In the Wenlock Limestone, Eastnor (2), TJsk(l),and Ledbury (1). 



