﻿216 BRITISH FOSSIL CEPHALOPODA. 



of its general shape and the position of its siphuncle. The section has flatfish sides 

 and a round front. If ever there were any ornaments, they are now utterly 

 obscured. The septa are a little undulating, and distant less than 1-|- the whorl- 

 breadth. The siphuncle is external. Diameter about 5 inches. 



Relations. — This has the proportions and absence of ornament of T. speciosum, 

 but the section is flatter and the septa more remote and undulating. 



Distribution. — This specimen is from the Durness Limestone in Sutherlandshire, 

 which is on the horizon of the Lower Llandeilo. It was collected by Mr. C. W. 

 Peach, who informs me that he has seen some in situ of more than 6 inches in 

 diameter. The characters are so obscure, that from any other locality it would 

 scarcely be worth notice, but the presence of a Trochoceras or Lituites of any kind in 

 these early rocks is an important and interesting fact. 



Trochoceras (?) cinereum, Blake, PI. XX. fig. 2. 



1843. Phragmoceras compressum, Portlock, ' Geol. Report,' pi. 28b, fig. 2, p. 282. 

 Not Phragmoceras compressum of Sowerby. 



Type. — The whorl is not complete, but the species appears to be a Trochoceras, 

 by its great curvature and its want of symmetry. The rate of increase is great, and 

 the last whorl is equal to or greater than \ the diameter. The section is oval, the 

 greatest thickness being near the outside — approximately the thickness is ^ the 

 breadth — but it may have been compressed. The surface shows very peculiar 

 ornaments. They are fine clearly drawn alternate riblets and striee of equal size, 

 from 3 to 4 per line, which start out straight from the inner edge of the whorl for a 

 little way, then bend backwards very rapidly and become almost longitudinal, and 

 finally bend out again to pass straight over the back at a point nearly as far behind the 

 inside edge as the breadth of the whorl. Towards the aperture the curve becomes 

 convex forward before the backward turn is taken, which is thus reduced in length. 

 The aperture is parallel to these lines and is not contracted. These lines are not, 

 however, simply lines of growth, they are ornaments. The septa are pretty convex, 

 and separate about -^ the diameter. The sutures are nearly direct. No siphuncle 

 is seen. Diameter about 4 inches. From a light ashy bed, referred to the Bala 

 Series at Desertcreat. In the Museum of Practical Geology. 



General Description. — Two other examples only of this very curious form have 

 been seen from the same locality. They both show the same general shape, and the 

 peculiar sigmoid ruled lines upon the surface, which however die away in parts. 

 One of these is the figured specimen, in which the want of symmetry is not well 

 marked, neither is the completion of a whorl. The others, those less figurable, are 

 more decisive on these points. 



