ANTHRACOMYA ADAMSII. 89 



1. Antheacomya Adamsii, Salter. Plate XII, figs. 1 — 19. 



Antheacomta Adamsii, Salter. Geol. Surv. Mem. Iron Ores S. Wales, 1861, p. 230, 



pi. ii, figs. 7, 7 a, lb. 

 Ncm — Ward. North Staff. Inst. Min. and Mech. Engineers, 



vol. x, 1890, p. 125, pi. i, fig. 2. 

 — — Hind. Quart. Journ. Geol. Soc, vol. xlix, 1893, p. 260, 



pi. viii, figs. 5, 5 a, 6, 7, 8. 



Specific Characters. — Shell equivalve, obliquely and triangularly ovate, 

 compressed all round tine borders, and produced posteriorly. The anterior end 

 is short, narrow in depth, only slightly convex, with a straight superior margin 

 and a rounded border, the antero-superior angle being a rounded right angle. 

 The inferior border descends rapidly, being at times slightly situated anteriorly ; 

 otherwise the outline is more or less convex. The posterior end is flattened and 

 expanded, with a more or less truncated border. The hinge-line is straight, 

 extending nearly the whole of the length of the shell ; its umbones are broad, 

 tumid, contiguous, raised above the hinge-line, situated in the majority of cases 

 at about a point equal to two-fifths of the length of the hinge-line from the anterior 

 end. The posterior slope is much compressed, and produced upwards. An 

 oblique obtuse swelling passes diagonally backwards and downwards from the 

 umbo, and soon becomes lost on the surface of the shell, anterior to which is 

 an almost obsolete broad sulcus. The lunule is elongate and narrow. The carti- 

 lage is external, very small and erect. The hinge-line has not yet been observed. 



The interior is smooth ; muscular scars normal in position and arrangement. 



The exterior is marked with fine excentric lines and folds of growth, which 

 are crowded together at the anterior end, but diverge slightly as they pass across 

 the shell, becoming parallel to the lower margin, the curvatures increasing in 

 strength as they approach the posterior end, where they are reflected upwards to 

 terminate in the superior border. Obsolete radiating lines are often seen on the 

 posterior slope. Periostracum strongly wrinkled, shell thin. 



Dimension* (PI. XII, fig. 1) : 



Antero-posteriorly . . . .65 mm. 



Dorso-ventrally . . . .45 mm. 



Laterally . . . . .10 mm. 



Localities. — Soap vein, Pen-y-cae, South Wales. Little Mine ironstone of 

 Fenton and Longton, which is the same bed known as the New Mine, or 

 Burnwood, of the more northern part of the North Staffordshire Coalfield. 

 Horsleywood seam, Northumberland. 



Observations.— Like other Coal-measure shells, the shape of Anthracomya 

 Adamsii is not very constant even locally. The whole of the specimens of this 



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