﻿138 BEITISH FOSSIL CEPHALOPODA. 



slightly. It might also be taken for 0. ludense, but its lines of growth are really 

 ornaments, and its rate of increase is greater. It has no relation to the specimens 

 called 0. Brightii, which have been referred to it, except that the siphuncles of both 

 have been figured, though essentially dissimilar. 



Distribution. — In the Lower Ludlow of Mocktree (2) and Ledbury (2) ; in the 

 Aymestry Limestone of Usk (5) ; in the Upper Ludlow of Ledbury (2), Under- 

 barrow (1), and Brigsteer (1). 



It is also recorded by Salter, from the Wenlock Limestone of Ledbury. 



Orthoceras revehsum, Blake, PL XL fig. 7. 



Type. — The specimen is flattened, and the breadth as thus seen increases at the 

 rate of 1 in 5. No characters, either of body-chamber or septa, are seen. The 

 ornaments consist of very remarkable transverse, nearly direct downward imbrica- 

 tions. These are somewhat irregular, and are alternately stronger and weaker ; but 

 each one, as traced round the circumference, is weak in one place and strong in 

 another ; they are yg- the diameter apart. The diameter is 1^ inches, and the length 

 about 1 inch. In a mudstone, probably Ludlow matrix ; locality unknown. In the 

 Museum of Practical Geology. 



General Description. — Two other specimens show the same remarkable ornaments, 

 but give no further information. The imbrications are downwards, and distant -^ 

 to ^ the flattened diameter, and are thus wide enough apart to give a ribbed aspect 

 to the shell, the intervening spaces being prominent. One of these presents a 

 somewhat spotted appearance, as if some membrane had covered it. 



Relations. — This species is nearly allied to 0. Maclareni, to which the specimens 

 in question have been referred, but the imbrications are distinctly downwards, and 

 are nearly direct ; they have also a peculiar form and irregularity of development 

 which entirely distinguishes them. 



Distribution. — The only certain locality is the Lower Ludlow of Leintwardine (1). 

 The other specimens are from the Wenlock Shale ? of Llanbadarn (1), and the Upper 

 Ludlow ? of unknown locality. 



Section Losves. 

 Orthoceras sericeum, Salter, PI. XIII. figs. 1, 2. 



1866. Orthoceras sericeum, Salter, 'Memoirs of the Geological Survey,' vol. iii. pi. 10, 



figs. 4, 5, p. 356. 

 1873 - » „ Salter, ' Cambrian and Silurian Fossils,' p. 18. 



1873. Orthoceras, sp., Hicks, 'Quart. Journ. Geol. Soc' vol. xxsix. pi. iii. fig. 27, p. 51. 



Type. — Two specimens are figured by Salter, both of them flattened in the slate. 



