308 CARBONIFEROUS LAMELLIBRANCHIATA. 



grande ressernblance avec le Broeclda Kayseri, dont les crochets sont plus petits, 

 le cote posterieur plus allonge, et les bords plus arrondis." I do not think that 

 the characters here relied upon for specific determination and for the erection of 

 four species are more than the normal amount of variation to be found in a 

 species which attains a large size. It may be mentioned that de Koninck states 

 that the whole four species occur at one horizon, that is, in his etage II. With 

 the exception of B. prisca, all the others are said to be rare. 



For such a large shell the groove for the external ligament is very small, and it 

 is very probable that, as in other members of the family Edmondidse, there was 

 some internal ligament, for the muscle-scars are very shallow and inconspicuous, 

 and do not show any indications of great strength. 



I have no doubt that the shell described as Myacites ? tenuilineata by R. 

 Etheridge, jun., is a somewhat undergrown example of Portlock's species. This 

 is the only Scottish example of the species that I know. Mr. Etheridge states, 

 " Surface with numerous close, thin, concentric lines, which here and there show 

 traces of granulation." Further on he says, "With a good lens traces of the 

 granulation can be detected. This would still further tend to ally it with 

 Myacites." This author was probably not aware that this character had been 

 shown to be present in Edmondia by King. 



Edmoxdia gigantea, de Kan inch, sp., 1885. Plate XXX, figs. 4, 4 a. 



Broeckia gigantea, de Koninck, 1885. Ann. Mus. Eoy. d'Hist. Nat. Belgique, 



torn, xi, p. 22, pi. v, figs. 1, 2. 



— dephessa, de Koninck, 1885. Ibid., p. 22, pi. v, figs. 7, 8. 



— subjeqtjalis, de Koninck, 1SS5. Ibid., p. 21, pi. iii, figs. 19, 20. 



Specific Characters. — Shell large, ovately rhomboidal, compressed, only slightly 

 convex, inequilateral ; the anterior end is small but deep, rapidly compressed into 

 the edge of the valve, especially at the antero-superior angle, which is erect and 

 bluntly angular. The anterior border is regularly rounded, and passes with a 

 sweep into the ventral edge, which is only slightly convex, and subparallel with 

 the dorsal border. The posterior border is almost truncate and subquadrately 

 rounded at each extremity. The hinge-line is long and gently arcuate. The 

 umbones are elongate, compressed, small, strongly incurved, and twisted on 

 themselves, contiguous, and situated in the anterior quarter of the valve. They 

 are raised above the hinge-line, and are well marked off from the valve in front, 

 where they are on a much higher level than the front part of the hinge-line ; but 

 behind they form a compressed elongated swelling on each side of and above the 



