﻿288 GASTEROPODA OF THE INFERIOR OOLITE. 



220. Amberleya, sp. ; cf. Trochus anaglypticus, Miinster. Plate XXII, fig. 12. 



1844. Trochtts anaglypticus, Miinster. Goldf., Petref., pi. clxxx, fig. 4. 



It must be admitted that the details of ornamentation do not tally very well 

 with those of Goldf uss's figure, though, making allowance for difference of artistic 

 treatment, and of mineral conservation, there are some grounds for inviting com- 

 parison. Our fossil is unique from the "marl with green grains" at the base of 

 the Humphriesianus-zone of the Sherborne district. It may be merely a sport of 

 the very abundant Arab. Obornensis. 



221. Ambeeleya biserta, Phillips, 1829, Section A. Plate XXII, figs. 13, 14; 



Section B, Plate XXIII, figs. 1, 2. 



1829 and 1835. Teochtjs biseetus, Phillips. Geol. Yorks, pt. 1, pi. xi, fig. 27, 3rd edit. 



(1875), p. 259. 



18S4. The " Tbochxs " EisEETus-group, Hudleston. Geol. Mag., dec. 3, vol. i, 



p. 248, pi. viii, figs. 9—11. 



Bibliography, fyc. — Phillips's type was from the Dogger, and appears to have 

 been lost, but the original figure leaves no doubt as to what fossil is meant. Bean 

 recognised a species belonging to the same group, which in the second edition of 

 Phillips's work, p. 129, was quoted, without figure or description, as Turbo 

 unicarinatus, Bean, MS., and in the third edition, p. 258, as Littorina unicarinata, 

 Bean, MS. 



We have actually in the present case four different forms to deal with. A 

 form like PI. XXII, fig. 13, was originally described by me as Littorina biserta, but 

 I now consider it to be the earlier stage of Amberleya (Trochus) biserta (PI. XXII, 

 fig. 14). Those who have followed me thus far in dealing with Amberleya will be 

 fully prepared to believe in the modification of the aperture from an ovate and 

 almost Purpurina-like aperture (fig. 13) to a subcircular or almost trapeziform 

 aperture (fig. 14). These two, then, are merely varieties of age, and constitute 

 our Section A. That there is an analogous relationship between Littorina 

 unicarinata (PI. XXIII, fig. 1) and the larger form (PI. XXIII, fig. 2) is also 

 probable, though not quite so clear, owing to imperfectly preserved apertures, 

 and to the slight flattening out of the smaller specimen. It might, perhaps, be 

 possible to separate them specifically from the more typical forms of Amb. 

 biserta, but at present it seems safer not to do so. This, then, constitutes our 

 Section B, which includes the Littorina (Turbo) unicarinata of Bean. 



