﻿LITTORINA. 



299 



234. Littoeina Dorsetensis, sp. now, or ? var. of Litt. gedilis. Plate XXIV, fig. 



3 (A), fig. 4 (B), fig. 5 (C). 



Cf. for B Trochtts gbanaeius, Heb. and Desl. Foss. Montreuil-Bellay, p. 53, 



pi. ii, fig. 8. 



Description, A and B : 



Length ..... 14 — 17 mm. 

 Length of body-whorl to total height . . say 50 : 100. 



Spiral angle (convex) . . . 60°. 



Shell irregularly conical, spiral angle usually convex. Whorls seven, narrow, 

 flatfish, or slightly biangulated ; suture well marked, rarely gaping. Within 

 certain limits there is considerable variety, some shells being more trochiform, 

 others more turbinate. Apex sub-obtuse, the two apical whorls being smooth and 

 full ; in the rest of the spire and body-whorl there are three nodose spirals, the 

 nodes being rather wide apart, decussated by short, thick, axial ribs. The base 

 is rather flattened, with five or six plain spirals. Fine axial strise throughout. 



Occasionally a fourth spiral is developed (fig. 4), in which case we seem to 

 have the most characteristic features of Trochus granarius, Heb. and Desl. 



Aperture sub-orbicular, with an extremely short and straight pillar lip, which is 

 rounded off at the anterior extremity instead of being produced. 



Variety G. — Shell thin, eucycloid ; whorls biangulated, sutures rather gaping ; 

 spiral ornamentation much subdued, axial stria3 conspicuous and very oblique. 

 Pillar-lip rather longer than in vars. A and B, and the aperture less restricted 

 in front. 



In a large series of specimens every gradation between A, B, and C may be 

 noted. There are also specimens which approach " Turbo " centurio (Goldf., 

 pi. cxciv, fig. 7). 



Relations and Distribution. — The group of shells which I have focussed under 

 Litt. Dorsetensis is primarily related to Litt. sedilis. As a group given to sporting 

 it helps to show how " Littorina " and Amberieya seem to wait upon each other, 

 even to the thinning out of the shell-substance when the eucycloid character is 

 assumed. 



Extremely abundant in the concavm-zoxxe at Bradford Abbas. A few very 

 small specimens in the Pea-grit at Leckhampton. 



