C. p. Chaticin Sf T. H. Withers— Ftiuna of the Chalk Rock. 67 



averaging 1^ inches in diameter, are often found, and one large example 

 measuring 8 inches across has been recorded by Mr. H. Woods. ^ 



We have lately collected in the Chalk Rock at the Waterworks 

 Quarry, Marlow, Bucks, two completely septate portions of a fairly 

 large Ammonite which cannot be referred to either of the above- 

 mentioned species. 



In 1878 Bayle ^ instituted the genus Puzosia, but he gave no 

 diagnosis of the genus, and although he refers to it the three species 

 Puzona latidorsata, Michelin, sp., P. mayor iana, d'Orbigny, sp., and 

 P. planulata, J. de C. Sowerby, sp., he does not fix on either as 

 the type of his genus, a fact which has given rise to much mis- 

 understanding and confusion. The question has been discussed in 

 a work by Mr. G. C. Crick, ^ who gave a diagnosis of the genus Puzosia, 

 which is quoted below, and which we here follow. 



Our specimens agree well with this diagnosis, and are therefore 

 referred to the genus Puzosia. 



Genus PUZOSIA, Bayle. 



" Shell more or less umbilicated, with whorls more or less elevated ; 

 ornamented with forwardly inclined ribs which are continued over 

 the rounded ventral area but are absent near the umbilicus, also with 

 several forwardly-bent usually rather strong constrictions or varices. 

 Suture-line similar to that of Besmoceras but more reduced ; first 

 lateral lobe longer than the ventral lobe, lobes trifid and relatively 

 a little narrower than in Besmoceras, saddles almost alike, divided by 

 a rather deep lobule into two parts, each of which is subdivided as 

 in Desmoceras, several auxiliary lobes present, umbilical portion of 

 suture-line dependent."* 



The two specimens to be described are closely allied to the group 

 of Puzosia planulata, J. de C. Sowerby, sp.,^ the affinities of which 

 are fully discussed by F. Kossmat.® He considers P. planulata as 

 characteristic of the Cenomanian, from which horizon Sowerby's type 

 from Hamsey in Sussex came. He, however, does not incline to the 

 opinion that it has an extensive vertical range, and considers that 

 the forms from the higher horizons belong not to the same but to 

 allied species. 



Our two specimens come from a much higher horizon than 

 Sowerby's type, and although they are closely allied to Puzosia 

 planulata, differ in some respects from that species. We therefore 

 propose for these specimens, which in all probability belong to the 

 same individual, the name of Puzosia curvatistilcata. 



' H. Woods, "MoUusca of the Chalk Rock": Quart. Journ. Geol. Soc, 1896, 

 vol. lii, p. 80. 



- E. Bayle, " Explication de la carte geologique de la France," 1878, iv, Atlas, 

 pis. xlv, xlvi. 



^ G. G. Crick, "Cretaceous Fossils of Natal.— I. The Cephalopoda from the 

 Deposit at the North End of False Bay, Zululaud " : Third and Final Report 

 Geol. Surv. of Natal and Zululand, 1907, pp. 209, 213. 



* " That is, directed backwards, the lobes pointing across the whorl." 

 5 J. de C. Sowerby, Min. Conch., 1827, vi, p. 136, pi. dIxx, fig. 5. _ 



* F. Kossmat, " Untersuchungen iiber die Siidindische Kreideformation " : Beitr. 

 zur Pal. und Geol. Osterr.-Ungams und des Orients, 1898, Bd. xi, Heft iii, p. 112. 



