﻿142 BEITISH FOSSIL CEPHALOPODA. 



1870. Orthoceras lancea, Barrande, ' Syst. Sil. de Boheme,' pi. 379, 411, p. 640. 

 1870. „ lentum, Barrande, loc. cit., pi. 421-2, p. 641. 



Query 1843. Koleoceras pseudospeciosum, Portlock, ' Geol. Bep.' p. 380, pi. 26, fig. 3. 



1870. Orthoceras potens, Barrande, loc. cit., pi. 386, p. 540. 



Type. — The section is not well seen, the fossil being imbedded in the stone, but 

 it appears to be somewhat compressed. The rate of increase is 1 in 18, which 

 remains pretty constant throughout the length. No details of body-chamber can 

 be observed ; possibly it is not reached. The shell surface was probably smooth, 

 though it has been rubbed. The septa are direct, and distant throughout about 

 ^ the diameter, and their convexity is \ the same. The siphuncle is not properly 

 seen, and looks nearly central at the smaller end. In another specimen (fig. 2), 

 which was probably also used as type, the section is circular, and the siphuncle at 

 one end is ^ across the diameter, though central at the smaller end, and has itself a 

 diameter of -g- the whole, while the septa slightly undulate on the siphuncular side. 

 The larger of these specimens has a length of more than 18 inches, and its greatest 

 diameter is 1^ inches. From the Bala Beds of Glenwhapple, Ayrshire. In the 

 Woodwardian Museum. 



General Description. — Though several examples have a truly circular section, 

 most have the radii slightly unequal. The rate of increase is invariably slow, in 

 no example exceeding 1 in 11, and often much less than in the type. The body- 

 chamber was almost cylindrical, and appears to have attained a diameter of at 

 least 3^ inches, and perhaps more, though it is difficult to prove to what species 

 isolated body-chambers belong, even when occurring in the same beds with the 

 type. The septa are generally direct, as seen, but often show some undulation or 

 an obliquity up to 5°. Their distance is from ^ down to ^ the diameter, and is 

 only occasionally variable, but may be greater in youth. They have a convexity 

 of | to ] the diameter. The siphuncle is very nearly central in the young 

 shell (fig. 2a), but with growth it takes an excentric position -§- from the 

 side (fig. 2b) ; in some examples, whose axes are unequal, it is unsymmetrically 

 situated (fig. 8). Its diameter is from \ to -^ of the whole diameter, and it was 

 probably continuous. The type is the longest example known. The greatest 

 diameter of the septal portion is 1^ inches. 



Relations. — This species differs from O. vagans in the regularity of its septa 

 and the excentricity of its siphuncle ; it moreover increases less rapidly. The 

 difference between this and O. distans is not very great ; in the latter the septa are 

 always more than 1 the diameter apart, and in the present one that is their 

 maximum. The section also of O. distans is less circular, and it is a more 

 robust shell. Its excentric siphuncle differentiates this from O. ludense and from 

 O. primosvum. It is stated in Sir R. Murchison's paper (loc. cit.) that Barrande 

 recognised the specimens described by Salter as one of the Bohemian species 



