348 GASTEROPODA OF THE INFERIOR OOLITE. 



281. Ataphrus, cf. lucidus, Thorent, 1839. Plate XXVIII, figs. 18 a, 18 6. 



1839. (Rotella) LtrciDA, Thorent, sp. Fide Cossmann, Etage Bath., p. 277, 



pi. vii, figs. 1, 2. 

 Cf. also Plocostyltjs typus, Geinmellaro. Faune Griuresi, p. 346, pi. xxviii, 



figs. 1 and 2. 



The specimen from the Oolite Marl of the Nailsworth district, figured in the 

 accompanying plate, is unique as far as my collection goes. It has a basal 

 diameter of 13 mm. ; ratio of width to height as 10 : 7. There is the possibility 

 that this may be nothing more than a megalomorph of Ataphrus heliciformis, 

 M. and L. D'Orbigny's figure of Trochus lucidus (' T. J.,' ii, pi. cccxiv, figs. 5 — 7) 

 differs from that given by Cossmann. 



282. Ataphrus heliciformis, Morris and Lycett, 1851. 



1851. ? Crossostoma heliciforme, Morris and Lycett. Great Ool. Moll. pt. 1, 



p. 73, pi. xi, fig. 8. 

 1863. Monodonta heliciformis, Morris and Lycett. Lycett, Suppl., p. 123. 

 Cf. also — ovulata, Keb. and Desl. Foss. Montreuil-Bellay, p. 58, 



pi. ii, fig. 9. 



Bibliography, 8fc. — Although originally described as a fossil of the Great Oolite, 

 the authors noted that G. heliciforme occurred in the middle division of the Inferior 

 Oolite at Leckhampton. Monodonta ovulata seems to occupy an intermediate 

 position between this form and the more abundant Ataphrus Isevigatus. 



Description. — In the majority of the specimens the basal diameter is about 10 mm. 

 or rather less ; ratio of width to height as 4 : 3, being slightly less depressed than 

 Ataphrus lucidus. 



The following is the original diagnosis : — " Shell smooth, turbinated, some- 

 what depressed ; spire small, but little elevated ; whorls rather convex ; aperture 

 elliptical." 



Relations and Distribution. — More depressed than Ataphrus Isevigatus, less so 

 than the preceding species. Occurs at Stoford in Dorset, but principally in the 

 Oolite Marl of the Cotteswolds, and in the Parkins oni-zone of Aston and Not- 

 grove. 



