﻿BRITISH FOSSIL CEPHALOPODA. 181 



General Description. — The example referred to this species presents so remarkable 

 an agreement with the above description in its size, its curvature, its rate of increase, 

 the characters of the septa and the sutures, that the details need not be repeated. 

 It has, however, suffered some compression, which has rendered the section a more 

 elongated ellipse, of .which the axes are nearly as 2 to 1. The ornaments are fine 

 raised lines distant \ line on the front, somewhat imbricating forwards, but with 

 their curvature backwards, making a sinus on the front. No longitudinal lines have 

 been observed. The whole is septate, and the sutures pass a little more forward 

 on the convex side than in Barrande's figure. The siphuncle is not well seen, 

 but seems to be of moderate size, and situated about halfway between the centre 

 and the convex edge. 



Relations. — This species, as Barrande remarks, has some resemblance to a frag- 

 ment of a Nautilus, but he has found a large example showing it to form less than a 

 complete whorl ; but in fact the rate of increase as compared with the curvature is 

 so great, or, in other words, the angle of the spiral is so small, that a complete 

 whorl would be of enormous size. We need not, therefore, really compare it with 

 the Nautili, and its general form and remote septa only allow of its comparison with 

 Cyrtoceras llandoveri, whose siphuncle at once distinguishes it. 



Distribution. — From the Lower Ludlow rocks of Ledbury (1), in the collection of 

 Dr. Grindrod. 



Cyrtoceras (?) eqtjisetum, Blake, PI. XXX. fig. 7. 



Syn. 1838. Phragmoceras nautilaceum (part), Sowerby in Murchison's ' Silurian System,' pi. 10, 



fig. 3 (not fig. 2). 



Type. — The section is doubtful, but at present the surface of the side exposed is 

 uniformly convex. The curvature is very great, the mean radius being 1^ inches 

 when the diameter of the whorl is about lj inches. Thus, though the specimen is 

 imperfect at the smaller end and there are no signs of contact of an earlier whorl, 

 the appearances are almost those of a coiled shell. The rate of increase is about 

 1 in 15, measured along the outer curve. The ornaments are very rough irregular 

 risings, curving rapidly backwards from the inner edge, and covered with parallel 

 irregular lines of growth. Possibly 3 inches of mean length belong to the body- 

 chamber. There is no sign of any change towards the aperture, which will be 

 similar to the. general ribbing, and therefore have a deep sinus on the front. The 

 septa are rather remote, being from \ to \ the present diameter of the whorl apart, 

 or 9 in the quarter circumference seen. The sutures curve rapidly forwards towards 

 the convex side, cutting across several lines of ornaments. The siphuncle is ex- 

 ternal. Its elements are much narrower than their length, and have a conical 

 shape, enlarging towards the aperture, and suddenly decreasing on passing each 



