﻿88 BRITISH FOSSIL CEPHALOPODA. 



from Coniston, are oblique with the ribs, and lie in the alternate interspaces, and 

 have the same convexity as in the type. The siphuncle, also, is seen to be central 

 and small. The greatest length seen is 2 inches ; the greatest diameter, 1 4 lines. 



Relations. — The statement that 0. ibex occurs in the Lower Silurian is doubtless 

 founded on examples of this species (M'Coy, ' Paleozoic Fossils,' p. 319). The ribs, 

 however, have not here the separateness of those of 0. tenuiannulatum, which is the 

 species meant ; and though in some the transverse lines are scarcely discernible, 

 in other associated examples they are equal to the longitudinal, which is only 

 the case in the young of M'Coy's species. Moreover the separation of the septa by 

 two rings is a feature which unites the Cumbrian examples to those from Ireland. 

 O.discretum, Barrande, from ktage F, is very closely allied, but the ribs are much 

 more pronounced and separate, and the cancellation is never equal in the two direc- 

 tions, while the rate of increase is less. 



Distribution. — In the Bala Limestone of the Chair of Kildare (4) ; at Bala (1) ; 

 and Cynwyd (3) ; and in Coniston Limestone (4). Also in the Lower Llandovery, 

 Haverfordwest (2 ?). 



Orthoceras Nicholiantjm, Blake, PI. III. figs. 7, 7a; figs. 8 and 15. 

 Orthoceras Nicholiantjm, Salter, on tablet in Cardiff Museum. 



Type. — The shell is now flattened in the stone, and the true section is therefore 

 unknown, as is also the true rate of increase, which is slow. The ornaments consist 

 of transverse, sharp, scarcely separate ribs, with an obliquity of about 5 degrees, 

 and about \ the diameter apart. These are crossed by sharp, separate, longitudinal 

 lines, which pass over the ribs, and slightly knot them at the crossing. They are 

 irregularly placed, and not all of the same size ; on the whole they are about three or 

 four times as numerous as the ribs. Besides these, there are extremely fine transverse 

 lines, five times as close as the longitudinal, and scarcely parallel to the ribs. The 

 septa are not seen where the ornaments are preserved, which part may be the body- 

 chamber ; but at the smaller end are a series of small butt-shaped bodies, representing 

 the apparently central siphuncle, and showing by their size that the distance of the 

 septa was about § line. The whole length seen is 3f inches, and the greatest 

 diameter is 7 lines. From the Lower Ludlow of Usk. In the Museum of the Cardiff 

 Naturalists' Society. 



General Description. — This is a delicate shell, whose general appearance is perhaps 

 better given by figs. 7 and 8, which may represent but one specimen, which shows 

 a rate of increase of 1 in 14 on the flattened shell. The ornaments are always 

 somewhat oblique, and are, when well preserved, acute and sub-separate, but may 

 be rounded on the cast ; they are from f- to \ the diameter apart. The minor 



