TROCHOCERAS. 87 



Description. — Shell medium-sized, mucli recurved, rapidly tapering, asymme- 

 trical. Height, upon a chord of 25 mm., subtending the concave side, 10 mm. 

 Section irregularly circular, the ventro-dorsal being as great as the transverse 

 diameter, and the longest diameter being in an oblique direction. Siphuncle 

 central near the apex, tending outwards half way towards ventral margin in the 

 upper chambers. Chambers rather broad, very concave. Surface covered with 

 numerous fine, rounded threads, about 1 mm. apart, which are crossed and inter- 

 woven with more numerous similar transverse striee, forming a fine network. Shell 

 encircled by large, but low, rounded, distant bulgings, which are visible dorsally, 

 but are more prominent on the ventral elbow, and rather less so on the back. 



Size. — Phillips's original specimen, which is about half a volution, measures 63 

 mm. in length, and about 30 mm. in the longest diameter of its widest end. 



Locality. — Wolborough. There are five specimens in the God win- Austen 

 Collection in the Museum of Practical Greology, three small specimens in the 

 Torquay Museum, and one in the British Museum. 



BemarJcs. — The material for defining this species is quite unsatisfactory. 

 Phillips's original type is much injured and obscured by matrix, and none of the 

 other specimens supply its defects, as for the most part they belong to the apical 

 region or the immature shell. In one, which is evidently a young shell and retains 

 the body-whorl, the apex is almost sharp, the contour of the ventral side a quarter 

 circle, and the siphuncle central. In the larger specimens, the siphuncle, where 

 seen, is midway between the centre and the margin. 



The specimen in the British Museum is Phillips's figured type of G. nodosum, 

 Bronn. I examined it carefully in company with Mr. Foord, and came to the 

 conclusion that it evidently is a member of the group of shells to which Tr. pulcher- 

 rimum, Tr. Vicarii, Tr. ohliquatum, Phil., sp., and Tr. reticulatum, Phil., sp., belong ; 

 and that it is in all probability identical with the present species. The specimen is an 

 obliquely crushed shell, with a decayed surface, and with very few distinctive marks. 

 The chambers are moderately narrow. The siphuncle appears to be ventrally sub- 

 central. Phillips's figure gives a very misleading impression of it ; the transverse 

 marks are really far less prominent than there shown, and, especially when viewed 

 in profile, they appear to be similar to those of the present shell. As far too as 

 can be judged in its crushed state, it seems to agree with it in outline. Phillips 

 identifies his C. nodosum with Spirula nodosa, Bronn.^ This, however, distinctly 

 differs in the transverse ridges being much fewer, straighter, and more horizontal, 

 the section much more transverse, and the siphuncle marginal. Hortolus 

 convolvens, Steininger (not Montfort)," is a synonym of Bronn's shell. 



1 1835, Bronn, • Letbsea Geogn.,' vol. i, p. 102, pi. i, fig. 4 ; and 1851, F. Eomer in Bronn's 

 ' Lethsea Geogn,,' 2nd edit., vol. i, p. 491, pi. i, fig. 4. 



2 1834, Steininger (not Schlotheim), ' Mem. Soc. Geol. Fr.,' vol. i, pt. 2, p. 370, pi. xxiii, fig. 3. 



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