﻿3L8 



GASTEROPODA OF THE INFERIOR OOLITE. 



graph. Hence there is a sort of natural tendency to identify the British forms 

 with Thorent's species from the Inferior Oolite of the Aisne. As regards the 

 form of tuberculation, Discohelix spinosus more nearly resembles it. The fossils 

 now under consideration merely represent a modified form of Discohelix spinosus on 

 a higher horizon, but they are flat atop and not biconcave : hence, according to 

 the distinction adopted, they belong to Straparollus ; and thus in structure, and 

 probably in habit of growth, they most nearly resemble the original Euomphalus 

 tuberculosus. From the fact of Morris having quoted " Bridport " as the locality, 

 I have very little doubt that he was referring to the form now under consideration. 

 Description : 



Diameter . . . . .15 mm. 



Height . . . . .5 mm. 



Shell depressed, discoidal; under surface largely excavated, upper surface 

 nearly flat or slightly concave. The whorls are quadrangular, with flattened sides, 

 which exhibit a very slight tendency towards contraction anteriorly. The 

 marginal keels are grossly tuberculated, both on the upper and under side ; on the 

 flanks of the body-whorl these tuberculations almost extend across. Spiral 

 ornamentation very faint ; stria? of growth conspicuous, perpendicular or curved. 

 Aperture quadrangular, spiral and axial diameters nearly equal. 



Relations and Distribution. — The affinities of Sir. tuberculosus-dexter have 

 already been partly discussed. It differs from the French fossil in its dextral 

 habit, and to some extent in the shape of the tuberculations. There are no 

 sinistral forms in the Inferior Oolite of this country, but Straparollus sinister 

 makes its appearance in our Middle Lias precisely as it does in France. Hence 

 it seems to me that a dextral habit in our shell is an important element of 

 difference. 



There are two specimens in my Collection from the I'arkinsoni-zone of Burton 

 Bradstock, besides one in the Jermyn Street Museum evidently in a similar matrix, 

 and another from (?) Dundry. Small specimens from Hook Norton (0 or upper 

 part of B of Mr. Walford's classification) approach the Burton Bradstock fossils, 

 though with a leaning towards Solarium disrnlnm, Morris and Lycett. There is 

 also a specimen from the Lincolnshire Limestone of Stoke Lodge, which in some 

 respects has more resemblance to Thorent's figure than any previously examined. 



251. Straparollus pulchrior, sp. nov. Plate XXV, fig. 9. 



Description : 



Diameter . . . . .20 mm. 



Height . . . . .6 mm. 



