ALARIA. 129 



It may be that the apical conditions of this specimen are really the same as those 

 of Var. A. There are no certain signs of a spine but rather of a spinous swelling. 

 On the whole there is probably no real difference between Var. A and Var. B, other 

 than what may be due to the preservation of different features in each case. 



50. Alaria : species or variety. (PI. VI, fig. 2.) 



Differs from the forms already described in the much coarser ornamentation 

 of the higher whorls ; the spiral lines, too, are stronger and wider apart and the keel 

 more salient ; the spiral angle is narrower, and there was an immense spine about 

 one-quarter of a turn above the base of the chief digitation. 



Founded on an imperfect specimen said to come from the Humphriesianus-zone 

 of Dorset. This I think may prove to be a distinct species. It possibly belongs 

 to the section of Alaria now under consideration, or it may be truly Didactyl, 

 since the character of the penultimate and antepenultimate is greatly that of the 

 trifida-grouip. Alaria dubia might do as a trivial name. 



Section 2. — Perfectly Didactyl. 

 a. The Myurus-group =the " Longicaudes " of Piette. 



51. Alaria subl^svigata, sp. nov. Plate VI, figs. 3 a, 3 b ; 3' a, 3' b. 



Cf. Alaria myurus, Deslonc/charnps, narrow variety. Hudleston, Geol. Mag., 



dec. iii, vol. i, p. 196, pi. vii, fig. 6. 



Description : 



Length . . . . .28 mm. 



Width of body- whorl to height of shell . . 44 : 100 



Spiral angle. .... 34° 



The points in which this species or variety differs from At. myurus, Desl., 

 are : — the general form is slightly more elongate in the majority of specimens, the 

 whorls are less tumid, and the position of the spine on the posterior keel is differ- 

 ently placed ; in this case being nearly three-quarters of a turn above the 

 commencement of the wing ; the anterior keel is also better defined on the side 

 of the columella ; the aperture is somewhat more triangular. 



17 



