544 DR WHEELTON HIND ON 



to be seen on the front part of the shell. These ribs form the middle layer of the shell, 

 and are joined by fine transverse trabeculse. 



Dimensions. — A. specimen measured : antero-posteriorly, 7 mm. ; dorso-ventrally, 

 10 mm. 



Localities. — Mulloch Hill, Lower Llandovery ; Craigens, Middle Llandovery. 

 Ireland, Cappacorcogue, Cong, Co. Galway. 



Observations. — A very interesting specimen, which has the same characters which 

 are so well marked in Conocardium hibernicum of the Carboniferous rocks. Several 

 specimens show the shelly fringe which was produced from the posterior border. This 

 part of the shell is well represented in M'Coy's figure, which, however, is decorticated 

 and shows the radiating ribs of the intermediate layer of the shell. Some half-dozen 

 specimens are in the Gray Collection, several of which show the shelly process, and, with 

 the exception of a single example, all are from Mulloch Hill. 



The Carboniferous form C. hibernicum shows no advance in development on this 

 much earlier forerunner. In the latter I have never found the long rostrum possessed 

 by many species of the genus. Whether there was one in C. pristis I cannot say, but 

 none of the specimens show that part of the valve. 



A third species, C. wquicostatus, Phillips, sp. (Mem. Geol. Survey U.K., vol. ii., 

 pt. i., pi. xvi. figs. 1, 2), is known from the Wenlock Limestones, Woolhope and Dudley, 

 which differs much in shape and ornament and absence of process from the Llandovery 

 example. 



I note that Morris (op. supra cit.) gives Salter as the author of the species 

 C. pristis. This is, of course, an error for M'Coy. 



Conocardium dipterus, Salter, sp., 1851. (PI. V., figs. 27-30, 30a.) 



Pleurorhynchus dipterus, Salter, 1851, Q.J.G.S., vol. vii. p. 175, pi. viii. fig. 6. 



Specific Characters. — Shell obliquely semi-trapezoidal, strongly keeled. The hinge 

 fine elongate, straight. Anterior end triangular, sub-acute, compressed. The valve is 

 divided into two unequal portions by a strong, blunt, oblique ridge which passes from 

 the umbo to the inferior border ; the portion of the valve posterior to it is shorter but 

 more gibbose than the anterior. The posterior margin is angular below, but above is 

 adpressed to form a small depressed horseshoe-shaped space bounded by a ridge ; within 

 this space the margin of the valve is swollen, and from its upper and median portion 

 springs an elongate, hollow, conical process. The umbones are small, keeled, incurved 

 and flattened on their posterior aspect. The shell gapes anteriorly, the lower margin 

 being thickened, its inner surface developed into a series of teeth and sockets, which are 

 smaller and more numerous from before backwards. 



Exterior. — On the anterior portion of the valve the concentric ribs are well marked, 

 and are crossed by radiating ribs of moderate size. On that portion of the valve in 

 front and behind the keel the radiating ribs are thick, wide apart, and concentric lines 



