542 MM. Foord and Crick — On Nautilus elegans, Shy. 



became serpentines. It might, however, still be affirmed that they 

 were crushed as peiidotites and were afterwards converted into 

 serpentines. I possess only one specimen of a peridotite modified 

 by pressure, but this lends no support to that hypothesis, and the 

 structure of the accidental constituents in the Cornish serpentines 

 does not appear to suggest it, so that I think we must seek for some 

 other explanation. 



It results then from this investigation that in a large number 

 of cases the direct effect of ' dynamometamorphism ' on a serpentine 

 is not to produce any marked mineral change, but only to reduce 

 the magnitude of the constituents and to impress upon them a linear 

 arrangement, more or less marked. Under ordinary circumstances 

 it does not appear to generate one of the soft unctuous talcose schists, 

 though such a change sometimes occurs. This, however, must be 

 accompanied, as stated above, by considerable chemical alteration, 

 because in olivine or serpentine (and in the rocks mainly composed 

 of these minerals) the silica and the magnesia are nearly equal in 

 amount; while in talc the former is about double that of the latter. 

 There is also a lower proportion of H.,0. Perhaps, in such cases, 

 some local cause may have given to the water a more distinctly 

 solvent action. 



III. — A Revision of the Group of Nautilus elegans, J. Sowerby. 



By Arthur H. Foord, F.G.S. ; 



and G. C. Crick, Assoc.R.S.M., F.G.S., 



Assistant in the Geological Department, British Museum (Nat. Hist.). 



OWING to the defective character of Sowerby's description and 

 figure of Nautilus elegans, the latter has been variously 

 interpreted, specimens belonging to other species having been 

 frequently referred to it. In the present paper we shall show what 

 is the true N. elegans, tracing the history of the type-specimen, 

 which we have been fortunate enough to identify in the collection 

 of the British Museum. This done, we shall proceed to describe 

 three other species, viz. N. elegantoides, d'Orbigny, N. Atlas, 

 "Whiteaves, and N. pseudoelegans, d'Orbigny, all evidently allied to 

 N. elegans, and forming with it a group of species which may be 

 appropriately called the " Group of Nautilus elegans." 



The identity of Nautilus elegans, J. Sowerby, has hitherto been 

 completely mistaken, owing to the uncertainty existing as to the 

 true character of Sowerby's fossil, the type of which had not been 

 recognized. 



The following is Sowerby's description of this species : " Gibbose, 

 umbilicate, with numerous linear, reflexed radiating sulci. About 

 two-thirds as thick as wide ; the septa are rather numerous, gently 

 waved ; the aperture is obtusely sagittate, with the posterior angles 

 truncated ; umbilicus small, perhaps closed." Respecting the type- 

 specimen Sowerby states, " This fine specimen was found in the 

 chalk marie, at Ringmer in Sussex, in 1814, by Mr. Mantell." 



It is undoubtedly Sowerby's type-specimen which Mantell figures 

 in his Fossils of the South Downs, tab. xx. fig. 1, and which he 



