114 GASTEROPODA OF THE INFERIOR OOLITE. 
Oolite is endorsed by Piette and Cossmann. The former figures a variety (op. cit. 
pl. v, figs. 6 and 7) from the Fuller’s Earth of Les Clappes, which is charac- 
terised by numerous slender longitudinals on each whorl. The same author (op. 
cit., p. 46) points out the difference between Al. hamus, Desl., and the fossil so 
identified by Morris and Lycett. 
Description : 
Length of good-sized specimens 3 . 25 mm. 
Width of body-whorl to length of shell. . 40:100 
Approximate spiral angle 32° 
Shell strongly turrited (muricated), fusiform ; apex blunt, but the apical angle 
only slightly convex, so that the general aspect of the spire is sharp. Number 
of whorls eleven; two and a half smooth and convex; remainder of whorls of 
spire very angular, the keel being slightly above the middle; longitudinal cost 
strong, regular, and numerous, for the most part sloping from right to left. In 
the majority of specimens from Burton Bradstock these costz are confined to 
the anterior area of the whorl and fail to reach the suture, but in some cases (fig. 
6 a) they extend across the keel. There are about five spirals above the keel and 
usually four below, exclusive of the keel. The body-whorl is bicarinate, with the 
keels plain, and the spiral ornamentation fainter in most cases; the posterior keel 
carries two spinous lumps, one situate half a turn above the wing and the other 
mid-way between these points. 
The aperture is triangular to trapezoidal. The wing is constituted by the 
continuation of the posterior or principal keel, and consists of one stout digitation 
proceeding for some distance at right angles to the axis of the shell and suddenly 
curving upwards, somewhat after the fashion of a hook (the sharpness of this 
curve not sufficiently shown in fig. 6 c); see also Plate VII, fig. 9. The wing 
scarcely overlaps the base of the penultimate. The delicate spiral ornamentation is 
continued on the wing, base, and canal-sheath, being faintly decussated by fine 
longitudinal lines. Canal broad, moderately long, and curved anteriorly, though 
not to any great degree. 
Relations and Distribution—As the type of the Monodactyls Alaria hamus 
constitutes a standard of comparison both for varieties and species. The Dorset- 
shire specimens most nearly approach Deslongchamps’ fig. 32. In the Normandy 
specimens which I have seen the wing appears to overlap the base of the penulti- 
mate somewhat more than in our English examples, and possibly the hook-like 
curve at the termination of the digitation is sharper, and the digitation itself 
shorter in the Normandy specimens. The individual figured (Pl. VII, fig. 9) is an 
unusually fine example. 
This species is most abundant in the Parkinsoni-zone of South Dorset, and 
especially at Burton Bradstock, whence nearly all our best specimens are obtained 
