ON THE FAUNA OF THE CAMBRIDGE GREENSAND. 485 



24. Supplementary Notes on the Fauna of the Cambridge Green- 

 sand. By A. J. Jukes-Browne, Esq., B.A., F.G.S. (Read 

 March 7, 1877.) 



[Plate XXI.] 



In a paper read before the Society in January 1875, I discussed 

 the relations of the Gault and Chalk Marl in Bedfordshire and 

 South Cambridgeshire, and endeavoured to show that the fossil 

 contents of the so-called Cambridge Greensand are for the most 

 part remanies and have been derived from the upper beds of the 

 Gault. 



The conclusions arrived at were briefly these: — that the Upper 

 Greensand does not extend further in a north-westerly direction 

 than West-end Hill near Cheddington in Bucks ; that stratigraphi- 

 cally the Cambridge Greensand is of no importance, being a mere 

 nodule-bed at the base of the Chalk Marl : that it rests uncon- 

 formably upon denuded Gault ; that a greater portion of the fauna 

 belonged originally to the Upper Gault ; that the remainder, really 

 belonging to the bed itself, are species proper to the Chalk Marl 

 rather than to the Upper Greensand. 



A full list of the species then known as existing in the formation 

 was appended ; and the derived forms were therein separated from 

 those presumed to be indigenous to the Greensand itself. This list 

 was mainly prepared from an examination of the large collection of 

 fossils in the Woodwardian Museum ; and my investigations resulted 

 in the determination of many species that were previously unnamed 

 in that collection, and in the identification of others which had been 

 wrongly named. All these species were separately noticed, with re- 

 marks upon their determination and synonymy. 



These observations, however, were by no means intended as an 

 exhaustive study of the fauna of the Cambridge Greensand. Many 

 specimens remained which it was not then possible to identify; and 

 some of them appeared to be altogether new and undescribed ; the 

 consideration of these was purposely deferred until I should be 

 able to obtain more information regarding them. 



Two years have now elapsed, during which I have had the 

 opportunity of inspecting many more specimens both from this 

 and from other Cretaceous beds ; and I am now better able, there- 

 fore, to offer some remarks upon these forms. 



At the same time it is with considerable hesitation that I venture 

 to name and place on record four species which do not appear to 

 have been hitherto described ; for I consider the establishment of 

 such new forms as a very serious matter, and one upon which too 

 much care cannot be spent. 



It was, I think, Professor Forbes who remarked that few are 

 aware how many species have been named from single and often 

 broken specimens. Now it is obvious that such species cannot be 



