346 DR WHEELTON HIND ON THE LAMELLIBRANCH AND 



transversely subovate. The anterior margin is deep and regularly rounded, passing 

 with uninterrupted curve into the lower border, which is also convex, but the segment 

 of a larger curve than the anterior margin. The posterior end is narrowed, obliquely 

 truncate, almost straight. The postero-inferior angle acute, the postero-superior obtuse. 

 The hinge line is short, very slightly arcuate. The umbones are large, gibbose, elevated 

 above the margin, incurved, and subcentral. Passing obliquely from the umbo to the 

 postero-inferior angle is a well-marked subangular ridge which separates the dorsal slope 

 from the convex portion of the valve. 



Interior. — The hinge plate is normal. 



Exterior. — The surface is ornamented in front by regular lines of growth, which 

 become less marked over the posterior portion of the valve. 



Dimensions. — PL I. fig. 24. Specimen No. Tl865 B , a right valve, measures: 

 antero-posteriorly, 26 mm. ; dorso-ventrally, 20 mm. 



Locality. — Stirlingshire, Torwood Glen, 2^ miles N.W. of Larbert, in a bed 9 to 10 

 feet above Castlecary Limestone; Linlithgow, river Avon, about 100 yards below the 

 Mill, right bank, at the bend where stream takes a northerly direction, about \ mile N. 

 of Avonbank. 



Observations. — This species is represented by a larger number of individuals than 

 any other in the collection. It is seen that amongst them there is a fair amount of 

 variation. The same thing is observed in the figures of the American types figured by 

 Meek. We can even match the larger form (fig. 1,/), doubtfully referred to the species 

 by Meek, amongst the Scotch specimens. There is certainly a much closer resemblance 

 to the Permian Schizodus obscurus than to any other British species ; but it would 

 seem to connect S. axiniformis, which ranges from the upper part of the Carboniferous 

 Limestone series (Redesdale ironstone) to the Coal Measures (Coalbrookdale), with the 

 later form. From the study of a series it would appear that, with age, the angularity 

 of the oblique ridge tends to disappear, and the posterior end becomes produced. 



? Anthracomya truncata, sp. nov. (PI. I. figs. 29, 30.) 



Specific Characters. — Shell small, triangular, compressed, rapidly expanded 

 posteriorly, greatest vertical and horizontal diameter equal. The anterior end is 

 short, its margin rounded. The inferior border descends rapidly, joining the long, 

 straight, obliquely truncate posterior border by an elliptical curve. The hinge line is 

 straight ; the longest transverse diameter of the valve forms a well-marked obtuse angle 

 with the posterior border. The umbones are small, slightly elevated and swollen, placed 

 at the junction of the anterior and middle thirds of the hinge line. The valve is 

 obliquely swollen, forming a well-defined but gradually diminishing rounded ridge 

 passing from the umbo towards the postero-inferior angle. 

 Interior. — Not exposed. 



