CUCULL^A. Ill 



describe a number of new forms in addition to those already described, or to 

 unite all in one single species. 



I should perhaps hardly have ventured upon the latter course had not my 

 own view been confirmed by the remarks of Mr. Townshend Hall, who has 

 collected at different times vast numbers of these fossils, and who remarked to 

 me, when first I saw his collection, that he thought they ought all to be united, 

 and that he had arranged several hundred specimens in one continuous chain. 

 He has since favoured me with the following note, which he made in 1877. 

 *' Between G. amygdaUna on the one hand, and G. angusta on the other, there are 

 various intermediate forms, to which the names G. Hardingi% unilateralism and 

 depressa have been given. Is G. Hardingii a good species ? G. unilateralis is the 

 mean between G. amygdaUna and G. trapezium." 



On examining the specimens at Barnstaple with me. Dr. Hicks expressed 

 himself as inclined to the same view. 



For the sake of definition it may perhaps be convenient to retain the five 

 names, amygdaUna, Hardingii, unilateralis, trapezium, and angusta for the classi- 

 fication of shapes, provided it be understood that no zoological import be attached 

 to them. 



In figuring the species I have attempted chiefly to show forms intermediate 

 between these named varieties. 



It may be observed that young shells are often flatter, and have smaller and 

 less prominent umbones. 



2. CucuLL^A DEPEESSA, Phillips. Plate XI, fig. 14 and Plate XII, figs. 2, 3, 3 a. 



1841. CucTJLLJEA DEPEESSA, Phillips. Pal. Foss., p. 42, pi. xii, figs. 71 a — c. 

 1841. — COMPLANATA, Phillips. Ibid., p. 214. 



1855. DoLABEA DEPEESSA, M'Coy. Brit. Pal. Foss., p. 394. 



Description. — Shell large, convex, slightly inequivalve and inequilateral, 

 variable in shape, trigonal. Hinge-margin short, straight, about one-third of the 

 length. Umbones prominent, incurved, rather distant, inclined somewhat forward, 

 and situated subcentrally. Cardinal area apparently rather broad and concave. 

 Anterior margin broad, prominent, and roundly convex. Inferior margin oblique, 

 nearly straight. Postero-inferior corner steeply rounded. Posterior margin 

 oblique, nearly straight, meeting the hinge-margin at a low obtuse angle. Contour 

 deeply convex on the line of greatest depth from umbo to the postero-inferior 

 corner; before which it slopes flatly out to the margins, becoming shghtly concave 

 near the anterior end of hinge-line ; and behind which it is almost perpendicular, 

 becoming concave to form a small angular posterior wing. Surface smooth? 



