﻿BRITISH FOSSIL CEPHALOPODA. 227 



General Description. — I have only seen two other specimens possibly referable 

 to this. In one the section is more elliptic, but the general proportions are the 

 same. The knobs in this smaller specimen are more remote, namely, at every third 

 chamber. The septa are ^ whorl-breadth apart. The other specimen which is figured 

 (fig. 6) is evidently young ; but from its shape it seems to indicate that the defect 

 from regular curvature in the larger ones may be natural. In none of these is the 

 position of the siphuncle seen. Salter states it to be internal. There is a specimen 

 bearing this name under his hand in the Museum of Practical Geology, with an 

 internal siphuncle ; but this I take to belong to his subsequently established species, 

 Trocholites planorbiformis. 



Relations. — No British form approaches this in the slightest. It is placed as a 

 Lituites from its general appearance ; but it may be a Nautilus, like the Discites of 

 the Carboniferous rocks, in which group indeed it might well be placed. 



Distribution. — In the Lower Llandovery Grrits at Blaen-y-cwm (1), Mandinam (1), 

 Llandovery (1). 



Genus Lituites. 



Lituites? arietinus, Barrande, PI. XXXI. figs. 4, 4a. 



1865. Trochoceras arietinum, Barrande, ' Syst. Silur. de Boheme,' vol. ii. pi. 17, 25, 103, p. 103. 



Type. — The specimens figured by Barrande show an inconstant curvature, the 

 outline being elongated in one direction, also a varying rate of increase. But the 

 last whorl is about \ the diameter, and the inner whorl is scarcely, if at all, in 

 contact. The elevation is very slight. The section is oval and flat on the front, 

 and the thickness is greater than the breadth, but the proportion is very different 

 in the three specimens. The body-chamber is more than half a whorl. The orna- 

 ments are transverse ribs, about 40 per whorl, sharp, separate, curving obliquely 

 backwards. They are obsolete on the front, and replaced there by lines of growth. 

 On the concave side they are direct. The whole is covered by parallel lines of 

 growth, and on the concave side are obscure traces of longitudinal lines. The septa 

 are direct, concave on the side, and rise towards the aperture over the front. The 

 siphuncle is a little exterior to the centre. Transverse epidermids are seen on the 

 cast. The type is from the zone E of Barrande, or Upper Silurian. 



General Description. — The English specimens referred to this species have a rate 

 of increase indifferent parts from 1.35 to 1.81, and a breadth of last whorl from .2 



2 g 2 



