﻿BRITISH FOSSIL CEPHALOPODA. 127 



seen. The plate in the chambers may perhaps be compared with the flat band seen 

 on the septa of 0. imbricatum. 



Distribution. — In the Tilestones of Horeb Chapel (4) ; in the Upper Ludlow of 

 Freshwater East (5) and of Usk (1). 



It is also recorded by M'Coy from Lower Silurian, Tonlegee, but this is perhaps 

 a doubtful identification ; also by Strickland, from the Ludlow Bone Bed near Lyne 

 Down. 



Orthoceras lesteatum, Hisinger, PI. VII. figs. 2, 11. 



1837. Orthoceras lineatum, Hisinger, 'Petrefacta Suecana,' tab. 9, fig. 9, p. 29. 

 1843. „ „ Portlock, ' Geol. Eeport,' p. 370. 



1846. ,, „ M'Coy, ' Silurian Fossils of Ireland,' p. 9. 



Syn. 1820. Orthoceras striatum, Marcklin, Hisinger, ' Anteneckoer V.' tab. v. fig. 1. (Not of 



Sowerby.) 

 1843. „ subcostatum, Portlock, ' Geol. Eeport,' pi. 26, fig. 6, p. 371. 



1852. „ striatopunctatum, M'Coy, 'Pal. Fossils,' p. 9. (Not of Miinster.) 



1852. „ laqueatum, M'Coy, loc. cit., p. 315. 



1873. „ „ Salter, 'Cambrian and Silurian Fossils,' p. 98. (Not of 



Hall.) 



Type. — Hisinger states only that his species has a cylindrico-conic shell, longi- 

 tudinally very finely striated, and the siphuncle central. His figure, however, shows 

 that the section is circular, and the tapering 1 in 8. The ornaments are sharp lines 

 about 60 or less in the circumference. The septa are direct, and have a convexity 

 of -^q their diameter ; the siphuncle is moderate in size. From the Lower Silurian 

 of Sweden. 



General Description. — This species has often been quoted from British strata, but 

 from the want of further details about the Swedish form, and the fragmentary state 

 of our own, the reference may be somewhat doubtful. Certainly there are examples 

 which differ in no important particular from the above description of the type. The 

 section may be circular, but is always flattened. The rate of increase is 1 in 7 to 

 1 in 10, decreasing to almost zero in the body-chamber, which has a length three 

 times its basal diameter. The aperture is bounded by a curve which has a forward 

 bend on the sides. The ornaments are sharp, raised, separate riblets on a flat surface, 

 which are angular on the shell and more rounded on the cast. In some cases there 

 appear to have been very fine longitudinal lines parallel to these. The riblets vary 

 in number from 36 to 44 per circumference, though in one example, possibly the 

 fragment figured by Portlock as 0. subcostatum, only 10 are seen on the surface 

 exposed. As this is not proved to represent the half circumference, we can scarcely 

 consider such to belong to a separate species. The septa are direct, their convexity 

 is considerable when flattened, and they are distant f , or less, of the diameter. The 



