﻿BRITISH FOSSIL CEPHALOPODA. 207 



Genus Ascoceras. 



Ascoceras Barrandei, Salter, PL XXYI. fig. 9. 



1858. Ascoceras Barrandei, Salter, ' Quart. Journ. Geol. Soc.' vol. xiv. pi. 12, fig. 7, p. 180. 

 1867. „ „ Salter in Murchison's ' Siluria,' Foss. gr. 63. 



Type. — Section at the base of the body-chamber, now much compressed, so that 

 the long diameter in the plane of symmetry is in the ratio of 5 to 2 to the short one. 

 The radius of curvature is about 1^ inches at first. The whole body-chamber has a 

 length, as preserved, equal twice its greatest breadth. The aperture appears simple, 

 and has a diameter \ the greatest breadth. The ornaments are acute, separate 

 riblets, as direct to the general direction as may be, varying in distance from 6 per 

 line at the base to 14 per line near the aperture. The ordinary septa have a 

 convexity of \ the long diameter. The sutures are straight, but oblique to the 

 general direction of shell, slanting back to the convex side. The siphuncle is 

 moderately large, and is situated \ the diameter from the convex side. The 

 sigmoid septa are not more than two in number, and their curvature is not great, 

 as they make an acute angle with the part of the shell above them on the concave 

 side. The second succeeds the first in a nearly horizontal direction. They occupy 

 a length of -fe the whole chamber. Length, 2\ inches; greatest breadth, 1 inch. 

 From the Upper Ludlow, Stansbatch, Hereford. In the Museum of Practical 

 Geology. 



General Description. — The four examples referred to this species all agree 

 closely with the above, in the general shape of section, the amount of curvature, 

 and the proportion of length to the breadth. In one is a slight depression round 

 the aperture. The ornaments vary in number, and their direction is seen to be of 

 no consequence, as they become more nearly direct on approaching the aperture. 

 In one example also, there is a line of fracture on the two sides of which the riblets 

 have a different direction, showing that the animal had the power of repairing its 

 shell ; over the surface are seen some transverse epidermids. Not more than one 

 sigmoid septum is seen in any other example ; it has the same greatly curved out- 

 line cutting the less convex side at an acute angle at the top. 



Relations. — When Salter wrote his description of this species, he had only 

 Barrande's figure of A. bohemicum, which was published in the Bulletin of the 

 Geological Society of France, to compare it with — the grand collection of plates 

 belonging to the ' Systeme Silurien de Boheme ' not having been published. He 

 was thus led to state that it was a larger and thicker species than A. bohemicum, 

 that the lines of growth were more oblique, and the septa more extravagantly 



