﻿176 BRITISH FOSSIL CEPHALOPODA. 



little backwards and meet in a rounded curve on the convex side. The length of 

 the body-chamber is not seen. The aperture is simple and parallel to the ornaments. 

 Very few septal characters are seen : one specimen shows the septa y 1 ^- the long 

 diameter apart, and the siphuncle, composed of spherical bulbs, on the outer curve. 

 In the rest the septa are either invisible, or the siphuncle has been displaced so as 

 to occupy the middle of the side. Greatest length, 3 inches ; greatest diameter, 

 16 lines. 



Relations. — The external peculiarities of the British forms are so faithfully 

 reproduced in those which Barrande has figured and described as Cyrtoceras quasi- 

 rectum, that, in spite of some minor differences, it seems proper to refer them to 

 that species. These differences are, first, that the siphuncle is bulbous in ours and 

 not so markedly so in the Bohemian ; secondly, it has only been seen external, 

 which is only the case in a variety of Barrande's; thirdly, the section, though 

 undoubtedly compressed, never makes any close approach to being circular. In 

 regard to the last two points, the forms figured as C. ambiguum, by Barrande, 

 approach nearer to ours, but not in regard to the first point. 



Distribution. — In the Wenlock Shale of the Usk district (12) and in the Wenlock 

 Limestone of the same district (1). 



Cyrtoceras plebeium, Barrande, PI. XIX. fig. 5. 



1848. Cyrtoceras plebeium, Barrande, ' Haid. Ber.' iv. p. 208. 



1866. „ „ Barrande, 'Syst. Sil. de Boheme,' pi. 109, 208, p. 525. 



Type. — The section is oval, the ratio of the diameters being as 8 : 7. The 

 curvature has a radius of about 1 inch. The body-chamber is a little longer than 

 its basal diameter, and the aperture is a simple curve. There are no ornaments 

 beyond lines of growth. The septa have a slight curve backwards on the side, and 

 forward on the convex border. They have a convexity of £ the diameter, and 

 are distant | the diameter. The siphuncle is almost external ; it is cylindrical, and 

 y 1 ^- the whole diameter. The length is about 2^ inches. From the beds Di, Ei, E2. 



General Description. — Some little specimens, flattened in the Wenlock Limestone, 

 agree, so far as their characters are preserved, with this species. They have a 

 curvature of about 1 inch radius, the diameter being -^ inch. The rate of increase 

 is about 1 in 6. The body-chamber is short, if the aperture is reached. The septa 

 are gently concave forward, and are distant ^ to T the diameter. No siphuncle is 

 preserved. The length is about l£ inches. 



Relations. — This gently-curved graceful Cyrtoceras cannot be confounded with 

 any other ; the nearest being C. macrum, which has less curvature, and is altogether 

 a stouter shell. 



Distribution. — In the Wenlock Limestone of Dudley (2). 





