﻿BRITISH FOSSIL CEPHALOPODA. 121 



General Description. — The specimens of this species usually occur flattened in 

 the stone, so that their true section is unknown. The rate of increase is usually 

 less than the type down to 1 in 10 only, as far as seen. The ornaments are often 

 well marked and sharp, but characteristically undulate so as to clearly cross the septa. 

 They vary in number from 6 to 11 per line. The septa are always close, 

 sometimes only \ the diameter apart. No siphuncular characters have been 

 satisfactorily determined. The greatest diameter seen is 1 inch. Like many of 

 these shells, examples occur which have been mended during life. 



Relations. — The large size, more rapid rate of increase, and the closeness of the 

 septa separate this from 0. elongatocinctum, whose riblets, moreover, are usually 

 more numerous. From 0. expansum, the closeness of the septa and the less 

 numerous riblets also distinguish it ; and the obliquity of the latter separates 

 it from the commoner 0. recticinctum. 



Distribution. — Examples occur in the Upper Ludlow of Ludlow (2), Aymestry (3), 

 Malvern (1), and Kendal ; also in the Aymestry Limestone (2), Ludlow, and in 

 the Upper Silurian of the Pentlands (1). 



Orthoceras recticinctum, Blake, PI. XL fig. 4. 



Query 1870. Orthoceeas centrale, Barrande, ' Syst. Sil. de Boheme,' pi. 438. (Not of Hisinger.) 



Type. — The shell is now flattened, and the present rate of increase is 1 in 12. 

 It is impossible to tell where the body-chamber commences, but it is probably 

 of considerable length. The ornaments are sharp transverse riblets, which are 

 on the whole direct, though they are not rigid, but liable to slight undulations, and 

 tending to group themselves : there are about 7 per line. The septa are direct and 

 parallel to the ornaments, and distant about \ the diameter. The siphuncle is 

 moderate and central. Length, 6^ inches ; greatest diameter, 10 lines. From the 

 Upper Ludlow, Ludlow. In the Ludlow Museum. 



General Description. — Very little can be added by other specimens to the 

 characters of the type. The apparent rate of increase in shorter fragments is 

 often 1 in 8. The ornaments are always characteristic in their sharpness and 

 general directness ; they vary in number from 7 to 10 per line. The septa are 

 not often seen, but are always direct and less than \ the diameter apart. The 

 type is the largest known. 



Relations. — This is really a very distinct species, and can only be confounded 

 with others when the obliquity of their ornaments is not seen or the slight 

 undulations of those of the present exaggerated. Examples have usually been 

 confounded either with 0. subundulatum, from which the character of the ornaments 

 at once distinguishes it, or with 0. elongatocinctum, which is a much nearer ally, 



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