﻿156 BEITISH FOSSIL CEPHALOPODA. 



General Description. — Another example with an unsymmetrical siphuncle is the 

 specimen referred to by M'Coy and Salter; this is more or less contorted, and the 

 peculiarity might be thought due to that circumstance. Those referred to this 

 species have elliptic sections, and the rate of increase is between 1 in 18 and 

 1 in 36 in the body-chamber. The latter shows a length 2-f its basal diameter. 

 The septa have a varying obliquity from 5° to 15° and some amount of undulation, 

 and are distant } to ^ the longer diameter, the later ones being closer than the 

 earlier. Their convexity is considerable, and is greatest at the siphuncle. This is 

 not seen in the other examples, which agree in other respects. If Sowerby's 

 figured specimen, called 0. imbricatum, is rightly referred here, the aperture was 

 oblique in a contrary direction to the septa, and was bounded by well-marked lines 

 of growth. The type is the largest example known. 



Relations. — Regarding the unsymmetrical siphuncle seen in three specimens as 

 not a mere individual peculiarity, we may separate the present species from 

 0. imbricatum by this feature, but, in addition, its rate of increase is much less 

 rapid, and the convexity of the septa is greater and their undulations more 

 irregular. It is on these latter accounts that Sowerby's specimen is referred to 

 this species rather than to the one he names. There are four species figured by 

 Barrande with unsymmetrical siphuncles, but they do not show the close septa, &c, 

 of the present. One example also, which I refer to 0. ludense, shows the same cha- 

 racter (see PI. X. fig. 5), but the amount of double excentricity is much less, and I 

 regard it only as an individual peculiarity, very likely brought about by distortion. 



Distribution. — In the Wenlock Limestone (?) of Dudley (1) ; in the Lower 

 Ludlow of Ludlow (2) ; in the Upper Ludlow of Ludlow (1), of Benson Knot (1), 

 and of Kirby Moor (1) and Kendal (1). 



Orthoceras ludense, Sowerby, PI. X. figs. 1, 3, 4, 5, 7. 



1838. Orthoceras ludense, Sowerby in Murcbison's ' Silurian Syst.' tab. 9, fig. 1. 

 1852. „ „ M'Coy, ' Pabeozoic Fossils,' p. 315. 



1857. „ „ Salter in Murcbison's ' Siruria,' Foss. gr. 62, fig. 2. 



1873. „ „ Salter, < Camb. and Sil. Foss.' p. 158. 



Syn. 1857. Orthoceras columnare, Boll, ' Arcbiv fur Mecklenb.' xi. pi. 1, fig. 3, p. 16. 



1866. „ temperans, Barrande, 'Syst. Silur. de Bobeme,' pi. 230, 382, 451, p. 658. 



1870. „ Dahli, Barrande, loc. cit., pi. 440. 



Type. — The section is circular, and the rate of increase, where the shell is 

 uncompressed, is 1 in 12. The whole is septate. The septa are direct, and have 

 no undulation. They are distant f the diameter, and have a convexity of the 

 same amount. The siphuncle has a diameter equal to half the septal interval, and 

 is situated -^ along the diameter. The diameter is nearly 2 inches. The second 



