ALARIA. 131 



Al. laevigata 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 . . . .40.° 



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 a turn 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. lavigata and Al. sublavigata 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 b and 4 c represent specimens from the clypeus-grit of the 

 Stroud district, which already present some slight differences. The specimen 

 fig. 4 c in many respects resembles one described by me (' Geol. Mag.' 1884, p. 

 197) from the Cornbrash of Scarborough as Al. myurus var. teres. 



Some might prefer to regard Al. laevigata, sublavigata, &c, merely as varieties 

 of Deslongchamps' species. 



b. The Trijida-growp = 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 various 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 



