﻿100 BRITISH FOSSIL CEPHALOPODA. 



longitudinal riblets, by which he would distinguish it from his 0. perelegans. 

 Sowerby, however, himself says nothing about them, and an examination of his 

 type has failed to show me any, though specially looking for them. Moreover, the 

 general character of the ribs is not the same. While, therefore, I agree with 

 Salter in recognising only one longitudinally ornamented species, I cannot call 

 it 0. ibex. M'Coy, describing some examples with longitudinal riblets as 0. ibex, 

 including Lower Silurian forms of different character, gave the present name to 

 those " with narrower and more sharply defined rings, considerably more numerous, 

 and with finer longitudinal striation." However, all the longitudinally marked 

 specimens that I have seen have the same narrow character of ribs. I conclude 

 there is only this one longitudinally ornamented species in the Upper Silurian, and 

 all those called 0. ibex on account of such ornament probably belong to it. No 

 Orthoceras with this kind of ornament appears among Barrande's numerous 

 Bohemian forms. The 0. vertebrale of Hall has angular ribs, and is much larger, 

 while it retains the transverse striation. The cancellated young forms referred 

 to this species have no satisfactory distinction in themselves from 0. velatum, and 

 might be taken to prove the presence of the latter in Upper Silurian rocks. My 

 interpretation, however, seems the more probable one. 



Distribution. — Examples have been examined from the Upper Llandovery, 

 Penlan (1 large) ; from the Lower Ludlow of Aymestry (2), Mocktree (8), View 

 Edge (1), Dudley (3), and Ledbury (1); and from the Upper Ludlow of 

 Mocktree (1), Usk (1), Ludlow (2), Kendal (1), Bircher Common (1), and 

 Builth (1). 



Haswell (loc. cit.) records a species under the name as found in the Upper 

 Silurian of the Pentlands. 



Orthoceras kendalense, Blake, PI. III. figs. 13, 13a. 



Type. — The section was perhaps originally elliptical, the ratio of the axes being 

 now as 11 to 8. The rate of increase of the longer diameter is 1 in 11. The 

 ornaments consist of subangular ribs, i.e. of ribs which on reaching the lowest level 

 begin at once to rise again, and are not very rounded on their summits. These have 

 an obliquity of 6°, and are distant f the longer diameter. No finer ornaments are 

 preserved. The septa lie in each hollow, and are therefore 6° oblique, and distant 

 f the diameter. Their convexity is about \ the diameter, and their surface retains 

 its vascular markings. The siphuncle is as nearly as possible central. The length 

 is 11 lines, and the diameter 4± lines. From the Upper Ludlow, Kendal. In the 

 Museum of Practical Geology. 



General Description. — The nearest approach to a circular section seen is in one 

 whose diameters are as 11 to 10, and in this the rate of increase is 1 in 10 ; but the 

 more flattened examples seem to have a less increase almost down to zero. As the 



