CONOCARDIUM ALATUM. 473 



CoNOCARDiUM ALATUM, de KoniYich, 1885. Plate LIU, figs. 3 and 5. 



CoNocAEDiuii ALATUM, de Eoninck, 1885. Ann. Mus. Ko)-. Hist. Nat. Belg., 



vol. xi, p. 118, pi. xix, figs. 26—29. 



Specific Characters. — Shell small, inequilateral, trigonal, acutely keeled. Body 

 of the valve deep, acutely angular, rapidly compressed both in front and behind. 

 The anterior portion forms a triangularly conical wing, separated from the body 

 of the valve by a well-marked, somewhat oblique groove, gaping at the narrow 

 extremity and along the lower border. The inferior margin slopes rapidly 

 downwards and backwards till it meets the groove separating the anterior wing 

 from the body of the valve, where it becomes suddenly bent downwards on itself 

 till it reaches the lower part of the body, where it curves upwards to join the 

 crest formed by the elevated vertical line of the opposing edges of the valves, 

 which bisects the posterior surface. The hinge-line is straight and produced, 

 and continuous behind with the upper part of the rostrum. 



The umbones are acutely carinate, pointed, incurved, contiguous, hardly 

 raised above the hinge-line, and the stump of the rostrum is present, appearing to 

 be subcentral. From the umbo proceeds vertically to the lower margin an acute 

 ridge, becoming broader and less angular below, which separates the lateral and 

 posterior surfaces of the valve. The posterior surface is cordate, large, convex, 

 with a median vertical ridge which terminates above in the base of the rostrum. 



The body of the valve is rapidly compressed in front of the keel ; length of 

 rostrum unknown. 



Interior. — Specimens show the characteristic details of the genus. 



Exterior. — The surface is covered with radiating ribs, few and further apart 

 on the anterior wing, closer and more regular but more curved on the posterior 

 surface. 



Dimensions. — PI. LIU, fig. 3, a specimen from Lesmahagow, in the collection 

 of the Geological Survey, Jermyn Street, measures — 



Antero-posteriorly . . . .15 mm. 



Dorso-ventrally . . . . 12'5 mm. 



From side to side . . . .12 mm. 



Localities. — England : the Carboniferous Limestone of Settle. Scotland : the 

 Lower Limestone series of Lesmahagow and Law, Dairy, Ayrshire. 



Observations. — This species is easily recognised by its peculiar shape and the 

 absence of an adpressed and flattened posterior surface, the strong vertical keel, 

 and the compressed, narrow, anterior wing. The specimens which have served 

 for the above description were all labelled C. trigonale, and, indeed, with justice 

 on the mere reference to the figure of this species ; but, unfortunately, the type of 



61 



