﻿150 BRITISH FOSSIL CEPHALOPODA. 



and young forms of 0. ludense, which have direct septa. The specimen named 

 by Salter 0. torquatum is a rubbishy surface fragment, showing transverse strise, 

 5 per line on the average, and tending to imbricate upwards, which may belong 

 to this or some other species, but is in fact utterly indeterminable. 



Distribution. — The typical form occurs in the Wenlock Shale of Denbigh- 

 shire (1), Flintshire (1), Llangynyw (1), Nantglyn (1), Llansannan (1), and Builth 

 Bridge (7) ; in the Denbighshire Flags, Cefnddu (7), and Corwen (2) ; in the 

 Coniston Grit, Helmknot (1), and in the Coniston Flags, Horton (1) ; in the Lower 

 Ludlow of Ludlow (1) and of Ledbury (1), and in the Upper Ludlow of Led- 

 bury (1) and Benson Knot ? (1) ; in the Upper Silurian of Kerry (7), Tipperary (1), 

 and Gal way (1). 



The var. antiquior occurs in the Lower Silurian at Kilnacreagh, Clare (1), 

 Desertcreat (9), and Fermanagh (5). 



The species, as 0. primcevum, is also recorded by Salter from the Upper Llan- 

 dovery of Nantglyn and Craig Hir, and from Coniston Flags, Kirby Lonsdale, and 

 the Grits at High Hollins ; also by Baily, from the Bala Limestone of the Chair of 

 Kildare, and from the Lower Silurian, Portraine. As 0. ventricosum it has also 

 been recorded by Davies from the Bala Beds of Bala and Corwen, and by Salter 

 from the Wenlock Shale, Bron Binion. 



Orthoceras subcontctjm, D'Orbigny, PI. XII. fig. 9. 



1839. Orthoceras conicum, Sowerby in Murchison's ' Silurian Syst.' 



1847. „ subconicum, D'Orbigny, 'Prodrome de Paleontologie,' vol. i. p. 2. 



Not 1837. Orthoceras conicum, Hisinger, 'Lethaea Suecica,' pi. 9, fig. 5. 



Type. — The section is not known, but the part preserved has a rate of increase 

 of 2 in 9 . There appear to have been no external ornaments. The whole specimen 

 is septate, the chamber being -| of the diameter apart, and having a convexity of 

 about \ the same. The siphuncular apparatus occupies altogether about ^ the 

 diameter, and is formed by many deposits on its membranes, and on the septa. 

 The latter rapidly decrease before reaching the former. The inner tube of the 

 siphuncle is contracted into a cruciform shape, and the outer coat was covered by 

 irregular deposits. The diameter is 1^ inches, and the length If inches. From the 

 Upper Llandovery of Tortworth. In the Museum of the Geological Society. 



General Description,. — The section appears to be not far from circular. The rate 

 of increase is essentially great, at least 1 in 5. No body-chamber has been seen 

 connected with the peculiar siphuncle of this species, but there are some specimens 

 having about this rate of increase coming from lower rocks which may belong to 

 it : these have signs of a constriction below the aperture. The septa vary in 

 distance with age, being ^ of the diameter when young, and increasing in closeness 



