﻿158 BRITISH FOSSIL CEPHALOPODA. 



inches in 15^ inches; a third reduces it to 17 lines in 13^ inches; a fourth reduces 

 it to 13 lines in 5£ inches ; a fifth tapers from 11^ lines to 9 lines in 17 lines, which 

 would reduce from 13 lines to 8 lines in 2| inches; a sixth reduces it from 8 to 4^ 

 in 3^ inches; and a seventh 3| to 1^ in 19, which will give about 2 inches for 

 the last portion. Adding these, we should have a shell whose length is 

 4 ft. 1\ inches ! Small specimens are very likely to be confounded with other 

 species in the absence of connecting forms. They are most probably to be 

 recognised in those whose septa are at least \ the diameter apart, and which have 

 strong shells and a central siphuncle. 



Relations. — M'Coy thought he had identified this with 0. distans when he 

 proved that its siphuncle was not always central ; but in the latter species the septa 

 are much further apart than they would be at the like diameter in our present shell. 

 On the other hand, such species as 0. gregarium (from which it cannot well be 

 distinguished when the shell is preserved) and 0. subgregarium, which are of 

 small size, differ by having the septa closer, while in 0. politum and 0. pri- 

 meevum they are more remote. So common and wide-spread a species as this is 

 not likely to be confined to England ; and though Barrande makes no attempt at 

 comparison, there is nothing of importance to distinguish it from his 0. temperans, 

 which, though figured with an excentric siphuncle, is stated also to have a central 

 one, or from 0. columnar e of Boll, with which Barrande has subsequently united 

 his 0. Dalili. 



Distribution. — In the Upper Llandovery of Bogmine (2) ; in the Wenlock Shale 

 of Usk (2) ; in the Wenlock Limestone of Dudley (4), Malvern (2), and Tort- 

 worth (1) ; in the Lower Ludlow of Ludlow (9), Leintwardine (4), Woolhope (1), 

 and Ledbury (4) ; in the Aymestry Limestone of Usk (2) ; in the Upper Ludlow 

 of Usk (1), Ludlow (3), Ledbury (1), and Kendal (1) ; also in the Coniston Grits 

 of Middleton (1), and in the Upper Silurian of the Pentland Hills (3) and 

 of Gal way (1). 



It is also recorded by Prof. Hughes from the Coniston Flags, and by Salter from 

 the Coniston Grits of Helm Knot, and from the Lower Ludlow of Coalbrookdale. 

 In Bohemia and in Sweden it is an Upper Silurian species. 



Orthoceras distans, Sowerby, PL XV. figs. 1, 2. 



1838. Orthoceras distans, Sowerby in Murchison's 'Silurian Syst.' pi. 8, fig. 17, p. 619. 

 Syn. 1866. Orthoceras migrans, Barrande, ' Syst. Sil. de Boheme,' pi. 212, 309, 348, &c, p. 643. 

 Query 1866. Orthoceras Thomsoni, Barrande, loc. cit., pi. 218. 



Not 1873. Orthoceras distans, Salter, 'Camb. and Sil. Foss.' p. 159. 



Type. — The section is elliptic, with the long diameter in the ratio of 14 to 13. 

 The fragment is too short to determine the rate of increase accurately, but it is 



