﻿160 BRITISH FOSSIL CEPHALOPODA. 



Orthoceras baculiforme, Salter, Plate XV. fig. 3. 



1852. Orthoceras baculiforme, Salter, App. A to M'Coy's * Pal. Foss.' pi. 1 l, fig. 27, p. vi. 



1852. „ „ M'Coy, 'Pal. Foss.' p. 315. 



1873. „ „ Salter, ' Camb. and Silurian Foss.' p. 187. 



Type.— The specimen figured by Salter is a fragment only of a shell of which 

 another portion is preserved in the Woodwardian Museum, which was, no doubt, 

 obtained at the same time. When these are placed together, as in fig. 3, they show 

 that the supposed peculiarities of the species are due to pressure. Though the 

 lower septal part is elliptical by compression, the body-chamber is pretty accurately 

 circular. The rate of increase, however, is very small, not being more than 1 in 32. 

 The body-chamber is four times as long as its basal diameter. It is covered by 

 undulating lines of growth, which are occasionally very clearly marked, and are 

 generally thrown into groups. No other ornaments are seen. The septa are 

 direct and have a convexity of \ the diameter, and are distant a little more than £ 

 the same. The siphuncle is very nearly central. The greatest diameter is 7 lines ; 

 and the length preserved, 4 inches. From the Upper Ludlow of Brigsteer. In the 

 Woodwardian Museum. 



General Description and Relations. — It is doubtful if any other example of this 

 species is known. The chief peculiarity about it is the extremely slow rate of 

 increase combined with its comparatively small size. The former of these features 

 prevents our associating it with 0. gregarium; and the latter, combined with the 

 greater remoteness of its septa, separate it from 0. perversum. It therefore remains 

 distinct in spite of the change of its characters. 



Distribution. — In the Upper Ludlow, Brigsteer, Westmoreland (1). 



Orthoceras omissum, Blake, PI. XV. figs. 9, 9a. 



Type. — The section is elliptical, the axes being in the ratio of 5 to 4. The rate 

 of increase in the long diameter is 1 in 20. No body-chamber or surface is seen. 

 The septa are greatly undulating on the broad side, but are not far from direct on 

 the whole. Their convexity is equal to their distance, which is more than \ the 

 longer diameter. The siphuncle is on the short diameter T 4 T across it, and has a 

 diameter i of the whole. The greatest diameter is 1^ inches, and the length is 

 5 inches. From the Upper Ludlow of Benson Knot. In the Museum of Practical 

 Geology. 



General Description— -The section is always elliptical, though often rendered 

 more so by pressure, till the ratio becomes as 3 to 2. The rate of increase varies 

 from the same reason between 1 in 15 and I in 26. In one example, not however 

 certainly of this species, the body-chamber undergoes a decrease, is 4 times its 



