110 GASTEROPODA OF TH ; -- INFERIOR OOLITE. 



Division I. The Monodacttls. 



27. Alakia arenosa, Hudleston, 1884. Plate IV, fig. 1. 



1884. Alaeia abenosa, Hudl. G-eol. Mag., dec. iii, vol. i, p. 198 (May), pi. vii, 

 fig. 7. 



Description : 



Length 1 . . . . .20 mm. 



Width of body-whorl to length of shell . . 31 : 100. 



Approximate spiral angle . . . 25°. 



Shell fusiform, turrited. Number of whorls about ten, apical ones unknown. 

 Each whorl has a median carina which is strongly tuberculated. In the upper 

 whorls this tuberculation is extended axially so as almost to reach from suture 

 to suture ; but in the last two whorls it is confined to the region of the keels. 

 The whorls are marked with rather strong spiral lines. The body-whorl carries 

 two keels ; the upper one is the strongest, and has tubercles very similar to those 

 on the penult ; the tuberculations of the lower keel are less strong. The nature 

 of the wing is uncertain, there being no outer lip preserved. 



Aperture ? ; canal long and moderately curved. 



Relations and Distribution. — Some of the peculiarities of the figured specimen 

 are partly due to matrix and condition of the fossil. Piette (op. cit, p. 23) 

 alludes to a variety of Bostellaria subpunctata, Miinst., figured by Terquem, which, 

 as regards the tuberculations of the lower whorls, may have some resemblance. 

 This was from the Opalinus-zone. From Al. Phillipsii this species differs in the 

 position of the longitudinal costulge, in the tuberculated keels of the body-whorl, 

 and in the slightly narrower spiral angle. 



Rare in the Dogger Sands (Opalinus-zone) this species is interesting as the 

 earliest example of Maria at present known from the Jurassic beds of Yorkshire. 



1 These measurements exclude the canal. Since all Alarice possess a more or less blunt apex, 

 with great convexity of the opening of the spiral angle, the " approximate spiral angle " of this and 

 subsequent measurements is intended to denote the mean angle of the spire without reference to 

 the apical whorls. 



