50 W. S. Hudleston — On the YorhsJnre Oolites, 



found with identical external characters on many horizons from the 

 Bajocian to the Corallian, might well belong to different genera- 

 according to the horizon which contains it, if the internal characters 

 could be known. In default of such evidence, they appear dis- 

 inclined to make even a specific distinction. The form is stated to 

 be abundant in the " calcaire a polypiers " of the Moselle (Upper 

 Bajocian), but rare in the Lower Bathonian of that district. 



^ Phasianella latitjscula, Morris and Lycett, 1850. 

 Genus Cekithium. 

 The species referred to Cerithium will be many, or few, according 

 to the view taken as to the arrangement and classification of a group 

 of shells, which are fairly abundant in the Dogger Sands and extend 

 somewhat sparingly, and with considerable modification, throughout 

 most of the succeeding fossiliferous horizons, to re-appear in great 

 abundance in the Coralline Oolite. The representative form of the 

 group is C. muricatum, Sowerby, which, like all "species" with an 

 extended range in time and space — in fact, like all common species — 

 has had numerous offshoots diverging from the main line, in which 

 more or less difference of ornament may be noted. 



The second group comprises a smaller and more finely ornamented 

 set of shells, where the sculpture is pretty regular, but where the 

 proportions of the spire vary materially. Cerithium Beanii, Morris 

 and Lycett, will cover most of these forms, which in Yoi'kshire are 

 confined to the Dogger and Sands, as far as I know. 



Besides these two groups are a few rare forms of extremely dis- 

 similar character which must find at least a temporary resting-place 

 under Cerithium ; though the companionship of such shells as C. 

 Comptonense, which most probably should be classed under Lycett's 

 subgenus Kilvertia, with such a shell as C. caninum, seems strange 

 indeed. 



1 1850. Phasianella latiuscula, Morr. and Lye. Gt. Ool. Moll. p. 117, pi. sv. fig. 16. 

 These authors describe and figure a fossil cast, stated to occur "near Scarborough," 

 under the above designation. Their figxire is very familiar to Jurassic palaeon- 

 tologists, and has a certain resemblance to the soi-disant Phammellas, of which 

 several species occur in the Bathonian Beds of the West Midland district. In the 

 Leckenby Collection there are no specimens which could fairly be referred to Morris 

 and Lycett's species, except such as have a strong resemblance to Nalica Bajocensis 

 {N. puncHira, Bean, Inf. Oolite variety). The specimen in the York Museum 

 referred to, "P. latiuscula''^ is exactly like Morris and Lycett's figure-, being a very 

 perfect internal cast of a Naticoid shell in the grey matrix of the Scarborough Lime- 

 stone, and having considerable resemblance to the shell of P. elegans, a species of 

 the Great Oolite of the West Midlands. But it is certainly misleading to institute 

 a comparison between the external form of one shell and the internal mould of 

 another, even in the case of un ornamented species. 



The ratio between the body-whorl and the whole spire in the cast known as 

 "P. latiuscula,''^ is as 50 : 100 ; in average forms of the shell of Nalica Bajocensis 

 this ratio may be taken as 60 : 100. Making due allowance for the difference which 

 is certain to exist between the external proportions of a shell and those of its internal 

 moulds, it is by no means impossible that "P. latitiscula" represents the cast of 

 Natica Bajocensis. 



As it may be necessary to publish a supplemental plate at the end of this Memoir, 

 I shall be very glad if any proof can be adduced in the mean time of the occurrence of 

 such a species as "P. latiuscula,''' as a distinct shell. 



