﻿BRITISH FOSSIL CEPHALOPODA. 231 



lock (1) and Dudley (1), and in the Lower Ludlow at Elton (1), Dudley (1), Lud- 

 low (3), Ledbury (1), Newton (1), Craig Yale (1), and Malvern (1). 



It is recorded also by Salter from Upper Llandovery (?) at Nant Grlyn, and from 

 Lower Ludlow, at Parkes Hall, and by J. F. Brown, from the Upper Silurian of the 

 South Wales area. These references, however, may be to 0. ibex or Cyrtoceras 

 extricatum. 



Ophidioceras geometkicum, Blake, PI. XVIII. figs. 16, 16a. 



Type. — The rate of increase is 1.5 and the last whorl .31 of the whole, the whorls 

 being just in contact. The last chamber leaves the earlier whorls for some space. 

 The character of the section is not seen. The aperture is bounded by sigmoid lines, 

 and has an inflation on the inner side, giving it a proboscis-like form. The ornaments 

 are subacute, separate ribs, which run radially, and appear to be lost on the front, 

 which has the same appearance of a keel as in Oph. articulatum. There are 32 per 

 whorl, but they die away on the straight portion, which has only lines of growth. 

 The whorl is crossed by a number of sharp spider-lines, which pass across the ribs 

 so as to transgress nearly a rib-interval in their passage outwards ; these are 8 

 per space. Diameter 1 inch. From the Lower Ludlow of Ludlow. In the British 

 Museum. 



General Description. — Two other specimens from different localities show the 

 peculiarities of this form ; the rate of increase being 1 .53, and the last whorl .33 of 

 the diameter. The aperture is seen only in the type. The ribs may be as few as 

 27 per whorl, and bend back towards the outside, but there is the same appearance 

 of a keel, probably due to a flat band, in all, and the remarkable thread-like lines 

 transgressing the ribs, 7 per space. No septal characters are anywhere seen. 



Relations.— -It may seem at first sight improper to separate this from Oph. arti- 

 culatum, which it so closely resembles. But the reason for this resemblance is 

 that they both belong to a small group of shells, characterised by nearly straight 

 ribs, and by a band along the front, but which show many minor differences by 

 which they may be distinguished. (See Barrande, ' Syst. Silur de Boheme,' pi. 45.) 

 The present species has a broader last whorl and greater rate of increase than any of 

 those referred to Oph. articulatum. The ribs are perhaps not quite so straight ; 

 and, above all, though specimens of the last named, with ornaments perfectly pre- 

 served, have been seen, they do not show the remarkable transgressive threads 

 of the present. 



Distribution. — In the Lower Ludlow rocks of Ludlow (1), of Ledbury (1), and of 

 Dudley (1). 



