352 GASTEROPODA OF THE INFERIOR OOLITE. 
ferous beds are on the horizon of the Upper Division of the Inferior Oolite. M. 
Cossmann records it as Bathonian on the strength of a single specimen. 
Description : 
Height of a large specimen : : . 13 mm. 
Width, the same : > fd mm. 
Shell smooth, almost polished, height ind Trice in most cases nearly equal ; 
spire convex with a very obtuse apex, sutures close. Number of whorls about five, 
convex, but not salient. Body-whorl large, more than half the entire height, 
smooth, convex, but pinched in towards the basal angle; base smooth and rather 
flat. Aperture circular and small, columellar denticle well developed, and 
situated near the anterior extremity. 
Variety (fig. 12) —This represents a form very abundant in the Parkinson- 
zone at Burton Bradstock, which has an average height of about 10 mm., the 
height being sometimes equal to, sometimes in excess of the width. It also 
possesses the ordinary characters of At. Acmon, except that the spiral angle is 
even more obtuse, and that it is very gibbous owing to the sudden change in 
that angle immediately below the apical whorls. There are also other and 
narrower varieties leading up to Ataphrus Acis. 
Relations and Distribuiion—There are some differences between the very 
variable species Just described and the typical Normandy shell. Not to multiply 
names, I include a considerable series under Ataphrus Acmon, which in this case 
must be considered as representative of rather than identical with d’Orbigny’s 
species. The horizon on which these English shells occur is, however, the same 
asin Normandy. They may be distinguished from Ataphrus Labadyei by the close- 
ness of the sutures and the want of convexity in the whorls, besides other points. 
Ataphrus Acmon is tolerably abundant in the Upper Division of the Inferior 
Oolite, and notably at Burton Bradstock. A narrow variety approaching 
Ataphrus Acis occurs in the Upper Trigonia-grit of Cold Comfort. A small and 
wide-based variety (fig. 15) occurs at Hook Norton. 
287. Arapurus Acts, d’Orbigny, 1850. Plate XXIX, fig. 14. 
1850. Trocerus Acts, d’Orbigny. Prod., i, p. 265. 
1852. — — —_ Terr. Jur., vol. ii, p. 277, pl. ccexiii, figs. 13—16, 
1873. ‘“Trocuus Ispersont,” Morris and Lycett. Tawney, Dundry Gasteropoda, 
p. 38 (25). 
Bibliography, §c.—The remaining shells of this group may be roughly gathered 
under Tvochus Acis, which occurs in the same localities and on the same horizon as 
