﻿208 BRITISH FOSSIL CEPHALOPODA. 



sigmoidal in outline. But, in fact, no specimen of the present species has been 

 found of anything like the dimensions of the Bohemian form, and the obliquity of 

 the lines of growth is well matched in the latter. The statement that the septa are 

 more sigmoidal in outline I cannot understand, as the sole valid reason for separat- 

 ing the two species is that the septa in the present are but two in number, and they 

 have nothing like so great a curvature. I can only account for the statement on 

 the supposition that Salter included with his species a specimen which, on the very 

 account of its more sigmoid septa, I refer to A. bohemicum, but which in this respect 

 agrees neither with Salter's figure nor with the other specimens to which he refers. 

 Our species may very well be the Ascoceras Norvegicum of Barrande, which also has 

 but two sigmoid septa, not very greatly curved, but that appears to be fragmentary 

 and is not figured, and in any case Salter's is the older name. 



Distribution. — In the Upper Ludlow, Stansbatch (1) and Ludlow (3). Salter 

 mentions one from Hale's End, Malvern. 



Ascoceeas bohemicum, Barrande, PI. XXVI. figs. 10, 10a, ]06. 



1855. Ascoceras bohemicum, Barrande, ' Bull. Soc. Geol. de France,' vol. xii. pi. v. figs. 20-28, p. 74. 

 1865. „ „ Barrande, ' Syst. Silur. de Boneme,' pi. 93, pi. 94, figs. 28-37, pi. 96, 



figs. 46-49, p. 354. 

 1877. „ „ Barrande, loc. cit.,pl. 494, figs. 14, 15, pi. 513, figs. 14-16, p. 97. 



Type. — Section oval, the long axis in the plane of symmetry in the ratio of 5 to 4, 

 the narrower end being on the convex side. The radius of curvature of the convex 

 side of a large specimen is 3f- inches, or nearly double the greatest breadth. The 

 total length is 2f times the breadth ; the aperture is on a produced cylindrical part, 

 and is half the greatest diameter in breadth. The ornaments are fine riblets, about 

 6 per line, rather varying in direction, but on the whole transverse to the general 

 direction of the shell ; there are also in well-preserved young shells some longitudinal 

 lines crossing them, and each riblet has finer parallel strige. The septa have a 

 convexity of \ their long diameter, and slope back with a straight suture towards the 

 convex side. The siphuncle is moderately large, is situated near the convex side, 

 and is surrounded on the septal surface by an elliptic depression. A longitudinal 

 section (pi. 513) shows the true nature of the sigmoid septa admirably : the siphuncle 

 rapidly diminishes in size and at the same time approaches the convex border, and 

 the back-curved necks of the siphonal portions of the sigmoid septa are well 

 seen ; and these portions are proved to unite into one plate, from which the first 

 sigmoid septum is continued. The sigmoid septa are 4 or 5 in number, and curve 

 round so as to meet the exterior in an obtuse or at least a right angle. They 

 succeed one another in a general vertical direction, and occupy all but the neck, in 



