ALARIA. 131 
Al. levigata is admitted to be non-existent, there seem some grounds for distinction 
in other respects. 
Description : 
Length of largest specimen . 35 mm. 
Width of body-whorl to height of shell . 54: 100. 
Spiral angle : : 2 WA0E 
Shell fusiform, elongate, about ten whorls ; apicals unknown. The spire is 
composed mainly of about five very convex whorls, which are covered by fine spiral 
bands separated by regular furrows. Towards the centre of the penultimate one of 
these spiral bands becomes conspicuous and forms a slight keel. The body-whorl 
is bicarinated ; the posterior keel, more salient than the other, gives rise to a strong 
spine a quarter of aturn above the base of the wing. The spiral ornamentation is 
very marked between the keels and in the base of the shell; as many as a dozen 
spiral bands may be counted between the keels, some of which are continued on 
the respective digitations ; a system of finer lines intervenes. The wing consists 
chiefly of two long, diverging digitations, which are subtriangular in section. 
Piette says that the posterior digitation forms the arc of a circle of which the 
centre is situated towards the point of the spire. 
The aperture is trapezoidal with a considerable callus on the columella; the 
canal is said to be long and almost straight, being barely curved at its extremity. 
Relations and Distribution.—The relations of this, the type species, to such 
forms as Al. levigata and Al. sublevigata have been already indicated. The possi- 
bility of some of these latter being immature specimens of Al. myurus has been 
intimated. It is very rare in the Inferior Oolite of England. One of the figured 
specimens (4 a) is from Dundry, and is by far the finest ever seen by me from 
English beds. Figs. 4.) and 4 ¢ represent specimens from the clypeus-grit of the 
Stroud district, which alr eady present some slight differences. The specimen 
fig. 4c in many respects resembles one described by me (‘ Geol. Mag.’ 1854, p. 
197) from the Cornbrash of Scarborough as Al. mywrus var. teres. 
Some might prefer to regard Al. levigata, sublevigata, &c., merely as varieties 
of Deslongchamps’ species. 
b. The Trifida-group = the ‘‘ Hamicaudes” of Piette. 
It is by no means easy to decide whether to admit as species the numerous 
forms of this widely spread group, which have received names from var ious authors. 
That its members vary considerably as to size and proportions in the same series 
of beds may be seen by inspecting the lower figures of PI. VI. At present it is 
