106 MOLLUSCA FROM THE GREAT OOLITE. 



CEROMYA SYMONDSII. Tab. X, fig. 4a, b. 



Testa ovato-ventricosd, umbonibus magnis obliquis incurvis, latero antico convexo, postico 

 subcompresso et elongato, basi curvato ; plicis concentricis regularibus tenuibus non nunquam 

 obsoletis. 



Shell ovately ventricose ; umbones large, oblique, incurved ; anterior side convex ; 

 posterior side rather compressed and elongated ; base curved ; concentric plications regular, 

 very delicate, not unfrequently indistinct. 



The general figure approaches C. concentrica, but it is more elongated, the umbones 

 being more oblique and anterior; the concentric plications are more delicate, and are 

 curved with a larger ellipse, they become undistinguishable near to the umbones. The 

 substance of the test is extremely delicate, so that the fine plications are frequently visible 

 upon the nucleus. The height of the shell is rather greater than the diameter through 

 both the valves, and one fifth less than the longitudinal diameter, a slight aperture exists 

 at the posterior extremity of the valves. 



Localities. Nuclei occur rather commonly in the upper portion of the Great Oolite 

 two miles east of Minchinhampton, but examples with the test preserved are very rare in 

 the shelly beds of Minchinhampton Common ; it also occurs in the Inferior Oolite of the 

 same district. 



The name in compliment to the Rev. W. S. Symonds, the Founder and President of 

 the Malvern Naturalist's Field Club. 



CEROMYA UNDULATA. Tab. IX, fig. 1, la, b. 



Testa ovato-oblonffd, tumidd ; umbonibus anticis elongatis sub-terminalibus, involutes; 

 latere antico anyusto, brevissimo ; postico lato, elongato ; margins superiore convexo, interdum 

 subundulato carind dorsali oblique instructo ; margine postico truncate ; inferior e subrecto ; 

 latcribus lineis obliquis, excentricis crebris regularibus tenuissimis ct undulatis ; basi et 

 margine postico plicis concentricis paucis irrec/ularibus. 



Shell ovately oblong, tumid ; umbones anterior, elongated, subterminal, and involute ; 

 anterior side narrow, very short ; posterior side much wider and elongated ; superior 

 margin convex but irregular, sometimes rather undulated, a keel or angle passes obliquely 

 from the umbones posteriorly nearly parallel to the superior border; the posterior margin 

 is truncated, the lower margin straight. The sides of the shell are covered with densely 

 arranged undulating fine lines, which are directed obliquely or excentrically from the 

 umbones towards the wide posterior border, but do not reach it, being decussated by a 

 few irregular concentric plications, which in advanced growth occupy the inferior and 

 posterior margins of the valves ; the supero-posterior angle separates the sides from a 

 narrow posterior surface which is destitute of the excentric lines. 



