﻿1861.] KIRKBY PERMIAN, SOUTH YORKSHIRE. 299 



pole immense quantities of young and probably rather dwarfed spe- 

 cimens are to be had, some portions of the limestone being literally 

 full of them ; and as all these specimens are testiferous, and many 

 of them in a perfect condition, they have afforded me a good oppor- 

 tunity for studying some of the variations of form and character to 

 which this species is subject. The following remarks are therefore 

 solely based upon these materials. 



The common form is usually as wide as long, with, a large body- 

 whorl, a short, depressed spire (which occupies less than half the 

 entire length), and a large umbilicus. The whorls are ventricose and 

 rather flattened behind ; the body- whorl increases rapidly and has 

 two prominent central ribs, bounded on each side by others of less 

 strength, which characterize the species ; the apex is obtuse ; the 

 aperture orbicular with a slightly refiexed pillar-lip. 



Many of the specimens are proportionally longer (the spire being 

 "drawn out a little and the body- whorl of less width), and have the 

 whorls rounder and the spiral ribs of uniform strength. 



Another variety is without spiral ribs, or with very faint indica- 

 tions of them, and has the whorls somewhat shelving behind, most 

 prominent a little below the median line, and well rounded in front, 

 with a narrow, flattish region bounding the suture. 



There are numerous intermediate forms that are more or less mo- 

 difications of the three noticed, whose differences they serve to con- 

 nect by numberless slight gradations. This is strikingly the case 

 with the differences observed in the strength of the spiral ribs, it 

 being possible to form series of specimens showing their gradual obli- 

 teration; .and so it is with the differences seen in the size of the 

 spire, and with those of the rotundity of the whorls. Indeed, it is 

 almost easier to pick out specimens showing some slight differences 

 than specimens which show none. 



The Hampole specimens invariably have a more obtuse apex than 

 those of Durham, the first and second whorls being flatter compared 

 with the succeeding ones. 



The generic position of this species, like that of several other Per- 

 mian univalves, is still somewhat uncertain. It has been placed in 

 Turbo ; and its general resemblance to the shells of that genus in- 

 duces me to allow it to remain there. Its resemblance to Littorina, 

 to which it has also been referred, is perhaps almost as great. And 

 it is only right to mention that the operculum of this shell has 

 never been found, which is better explainable on the supposition of 

 its being horny, like that of Littorina, than calcareous like that of 

 Turbo. There is, however, no instance on record of the operculum 

 of any of the Permian Gasteropods having occurred in England or 

 Germany. 



Log. Pontefract, Hampole Stubbs, Moorhouse, Pickburn, Brods- 

 w r orth, Conisborough, and Barnborough Cliff. Taken by Prof. 

 Sedgwick between Marr and Hickleton*; and by Prof. Phillips at 

 Aldfieldf. 



* Trans. Geol. Soc, 2nd ser. vol. iii. p. 118. 

 t Mon. Perm. Foss. of England, p. 205. 



