474 CARBONIFEROUS LAMELLIBRANCHIATA. 



C. trigonalc preserved in the Gilbertson Collection of the British Museum, 

 PI. LII, fig. 3, is without any doubt the young of G. hihernicum. 



De Koninck figured this characteristically shaped shell under the name 

 G. alatum, and his type appears to have been about the same size as that in the 

 Woodwardian Museum, PI. LIII, fig. 5. De Koninck states that this species 

 possesses a little tubercle placed between the umbones, a character which he has 

 observed in no other species of the genus. This tubercle is well seen in PI. LIII, 

 fisf. 5 a. Hall has observed a similar character in the American G. catastomum. 



Genus ChtENOCahdiola, Hohapfel, 1889, emend. Beushausen, 1895. 



LuNULACARDiCM, Baily, 1860. Expl. Sheet 142, Geol. Surv. Ireland, p. 19. 



— Hohapfel, 1882. Goniatitenkalk von Adorf, Palseontographica, 



vol. xxviii, p. 255. 

 Ltjnulocabdium (pars), Hall, 1885. Greol. Surv. New York, Pal., vol. v, 



pts. i, ii, p. 437. 

 CoN'ocAHDiUM (pars), Etheridge, 1888. Brit. Foss., pt. i, Palaeozoic, p. 281. 

 Ltjnulicabditjm, Miller, 1889. North American Greol. and Palaeontol., p. 486. 

 Ch^nocardiola, Hohapfel, 1889. Kalte von Erdbach-Breitscbeid, Pal. Abh. 



Dames and Kayser, vol. i. 

 — Beushausen, 1895. Abhand. Kouigl. Preuss. Geol. Landes- 



austalt, p. 364. 



Generic Gharacters. — Shell equivalve, inequilateral, triangular, oblique, truncate 

 behind. Border rounded in front and below, obliquely truncate behind. Umbones 

 pointed, inrolled, and twisted forwards. Lunule (?) large. Shell moderately 

 swollen in front, with a sudden angular ridge from the umbo to the postero- 

 inferior angle and a rapidly compressed dorsal slope. 



Interior. — Anterior adductor muscle-scar small, round, deep, placed just below 

 and in front of the umbo, overshadowed by a thickened hinge-plate. Posterior 

 scar not known. Pallial line simple. 



Hinge thickened in front, probably with teeth, with parallel striations 

 posteriorly. 



Interior marked with radiating ribs near the margin, with a smaller shorter rib 

 between each. 



Exterior. — The surface is ornamented with radiatino- ribs. 



Observations. — Beushausen has seen fit to amend and limit the genus 

 Lumdicardium, Miinster, and to remove certain shells from Lunulicardium to a new 

 genus, Ghsenocardiola {op. supra cit.), which I propose to adopt, as the characters 

 of the interior revealed by Baily's types are not those of the former genus. At 



