350 GASTEROPODA OF THE INFERIOR OOLITE. 



This variety (see PI. XXIX, fig. 6) is smaller and slightly less depressed than 

 average specimens of Ataphrus laevigatus. It is, I have no doubt, the form 

 identified (« Quart. Journ. Geol. Soc.,' vol. ix, p. 326) as Trochus Behis from Ponton. 

 Extremely abundant also at Weldon. The denticle is usually more conspicuous 

 than in the accompanying figure, where indeed it is scarcely noticeable. 



284. Ataphetjs obtoetus, sp. nov. Plate XXIX, figs. 7 and 8. 



Description : 



Width or basal diameter . . . 10 — 14 mm. 



Width to height . . . . 10 : 9. 



Shell smooth, thick and gibbous ; spire moderately depressed, and consisting of 

 about four or five whorls, of which the penultimate exhibits a remarkable bulge in 

 the anterior portion. Aperture circular and small, with a thick denticle on the 

 columella, succeeded anteriorly by a shallow pit. 



Relations and Distribution. — In many places where Ataphrus Icevigatus occurs 

 this form may also be noticed, though in fewer numbers. It is probably nothing 

 more than a gibbous variety of the common form. I recognise specimens of 

 Ataphrus obtortus from Dundry, Beaminster, Mapperton, Stoford, and also from the 

 Parkinsoni-zone of Burton Bradstock ; also in the Dogger. The interest consists 

 in the fact that this species gradually shades off into less depressed forms, which 

 are difficult to separate from gibbous varieties of At. Acmon. 



285. Ataphrus Labadyet, d'Archiac, 1843. Inferior Oolite varieties. Plate XXIX, 



figs. 9 and 10. 



1843. Teochus Labadtei, d'Archiac. Mem. Soc. Geol. France, vol. v, pt. 2, 



p. 379, pi. xxix, fig. 2. 



1850. Tubbo Labadtei, d'Arch. D'Orbigny, Prod., i, p. 301. 



1851. Monodonta Labadtei, d'Arch. Morris and Lycett, Great Ool. Moll., 



pt. 1, p. 68, pi. xi, fig. 2 ; and var., fig. 11. 

 1884. Ataphbus Labadtei, d'Arch. Cosamann, Stage Bath., p. 279, pi. vii, 



figs. 5—8. 

 Cf. also ? Monodonta l^vigata, Miinst. Goldfuss, Petref. Germ., pi. cxcv, fig. 5. 



Chbtsostoma Acmon, Laube (non d'Orb.). Gast. Br. Jura von Balin, p. 13, 



pi. iii, fig. 2. 

 Tubbo (Monodonta) l^vigatus, Sow. ; var. bellulata, Bean. Hudleston, 



Geol. Mag., dec. 3, vol. ii, p. 53, pi. ii, 

 fig. 4. 



