﻿BRITISH FOSSIL CEPHALOPODA. 101 



ornaments characteristic of the type appear to be those of the young shell, and 

 afterwards to change, the character of the body-chamber and aperture will have to 

 wait the discovery of some connecting specimens. These ornaments are very 

 peculiar, giving the appearance of a crinoid ; but in two examples showing them at 

 one end we find them changing with growth into a more rounded separate type. 

 They are generally oblique, as seen on the side, but appear undulating only when 

 seen on the ventral or dorsal surface, and vary in distance between ^ and ^ the 

 diameter. They are covered superficially in one example by 28 sharp transverse 

 riblets per interval. The septa are at the base of every interval, and are almost 

 always seen ; they are parallel to the ribbing, and their convexity is not more than 

 £ the diameter. The central siphuncle is also confirmed in other examples. The 

 greatest diameter at which these features are exhibited is 7 lines. 



Relations. — This species differs from 0. ibex in the character of its ribs and their 

 greater closeness. It differs from 0. adornatum in the latter characteristic alone, but 

 then the difference is great. It is with great doubt that I separate this from 

 0. Gothlandicum, Boll, ' Archiv fur Mecklenburg,' pi. 5, fig. 14, and Barrande, ' Syst. 

 Sil.' pi. 441, fig. 14, with which it agrees in the shape of its ribs and its general 

 form, and differs only in having a central siphuncle and its ribs more remote, 

 being thus related to 0. ibex as 0. Gothlandicum is to 0. dulce. 



Distribution. — In the Upper Ludlow of Kendal (2) and of Llechclawdd (1) ; in 

 the Aymestry Limestone of Usk (3), and in the Lower Ludlow of Mocktree (1). 

 Also in the Upper Ludlow of Ludlow, showing the ribs of angular character 

 changing into more separate ones, with the transverse riblets (1). 



Orthoceras adornatum, Barrande, PI. III. fig. 10. 

 1870. Orthoceras adornatum, Barrande, ' Syst. Sil. de Boheme,' pi. 353, figs. 7-9, p. 299. 



Type. — The section is circular, and the rate of increase is 1 in 18. The shape of 

 each septal chamber is such that the centre swells out into a subangular band, with 

 nearly flat slopes to the sutures : these are direct, and distant ^ the diameter apart. 

 The surface of each chamber has about 10 transverse lines. No siphuncle is seen. 

 The length is 2 inches, and the greatest diameter is 4^ lines. It is the only specimen 

 known, and is found in the band Ei of the Upper Silurian. 



General Description. — A solitary example in the Museum of Practical Geology 

 repeats these features very exactly, though the section is not seen, and the rate of 

 increase is, if possible, less ; the transverse riblets are not seen. The length is about 

 1 inch, and the diameter about | inch. 



Relations. — This differs from 0. tracheale, to which it has been referred in the 

 Museum Catalogue, by the wide separation of its septa, and the angular character of 



