﻿122 BRITISH FOSSIL CEPHALOPODA. 



if not an ancestor, but which has more numerous and finer riblets, often more 

 undulating and the septa more remote. 



Distribution.— In the Lower Llandovery, Helmsknot (1) ; in the Wenlock Shale 

 of Oernant (1), Coldwell (1), Dinas Bran (L), Dudley (1), Barrington (1), and 

 Llandewi (1) ; in the Wenlock Limestone of Usk (1) ; in the Coniston Flags (5) ; 

 in the Lower Ludlow of Ledbury (3) ; in the Upper Ludlow of Woolhope (1), 

 Ludlow (7), Ledbury (2), Malvern (3), Presteign (2), Mocktree (1), Builth (1), and 

 Benson Knot (1) ; and other Upper Silurian localities. 



Note. — There are two specimens in the Woodwardian Museum from the Lower Bala of Llandeilo 

 and Builth respectively (one of them named O. fluctuatum by Salter), which have so strong a resem- 

 blance to this that, had they occurred in Upper Silurian rocks, they would have been unhesitatingly 

 referred to it, but there are not sufficient characters preserved to prove their identity. 



Orthoceras pendens, Blake, PI. XI. figs. 2, 2a, and 5. 



Type. — Two examples, which undoubtedly belong to the same species, but give 

 supplementary information, may be combined as types. The section is elliptic, the 

 ratio of the diameters being as 5 to 4. The rate of increase is from 1 in 6 to 

 1 in 7. The body-chamber has a length equal to three times the longer diameter of 

 its base, and the aperture is simple without any change of growth. The ornaments 

 are sharp riblets parallel to the septa, and distant about 6 per line at a diameter 

 of 5 lines (fig. 5). The septa are from 8°-10° oblique on the shorter diameter, and 

 are distant about f the same line ; their convexity is equal to their distance apart, 

 and is at a maximum nearer the lower side. The siphuncle, which is moderate 

 in size and central, is thus not on the summit of the convexity, but on the longer 

 slope in the direction of the short diameter (fig. 2a). The length of the example, 

 which is all body-chamber, is 2f inches, and its greatest diameter is l£ inches. From 

 the Bala Series, Glencotho Quarry, Broughton. In the Museum of the Geological 

 Survey of Scotland. 



General Description. — Only one other example from the same locality has been 

 seen, which confirms generally, but adds nothing to, the types. 



Relations. — Belonging by its ornaments to the group of 0. tenuicinctum, it differs 

 from them all by the obliquity of the septa and of the ornaments being in the 

 direction of the shorter rather than the longer diameter. 



Distribution. — In the Bala Series, Broughton (3). 



Orthoceras Grindrodi, Blake, PI. IX. fig. 9. 

 Type. — The section is slightly elliptical, the diameters being in the ratio of 13 to 

 12. The rate of increase is 1 in 13. The ornaments consist of vertical sharp sepa- 





