44 CARBONICOLA, ANTHRACOMYA, AND NATADITES. 
and writes of them as ‘‘ maritime Unionidex ;” while the latter considers that the 
position of the accessory-muscle scar is diagnostic of Cardinia. But this is not 
so, for the position of this scar in Carbonicola is very different from that which 
obtains in Cardinia. In Carbonicola the scar is above that of the adductor, between 
it and the upper border of the shell; while in Cardinia the scar is internal to the 
adductor, and within the pallial area. Moreover the position of the anterior 
adductor is almost marginal in Carbonicola, and situated in the superior-anterior 
angle of the shell; while this is not the case in Cardinia. The hinge, too, in 
Cardima is totally different from that of Carbonicola, and is described by 
Woodward? as “ cardinal teeth, obscure, laterals 1—0, 0—1, remote, prominent.” 
Zittel,” Stemmann, and Doderlein® still retain Anthracosia as a sub-genus of 
Cardinia. Salter* hazarded the view that Anthracosia (Carbonicola) might be 
allied to the Myadx. He says, “ Anthracosia was, I believe, a burrowing shell. 
Among beds, where these fossils were the only bivalves, I have seen bivalve 
burrows answering to them in size. It had certainly a thick and wrinkled 
epidermis, as the Myadz have, and no eroded beaks as is common in Unio ; but the 
palhal line was simple and the valves close.” 
I have never seen specimens of Carbonicola, except perhaps occasionally and 
accidentally so, in an erect or vertical condition in the shales; they all lie with 
their long axes parallel to the planes of the bed, and they are often covered with 
Spirorbis ; both of which facts militate strongly against the view that they were 
burrowers. Indeed, I think that the characteristics of the Carbonicole show 
a close connection with lower forms, in the transverse articulating hinge-plate 
and the persistence of the striations formed by lines of growth both in the lunule 
and in the groove for the external ligament posterior to the umbo. The common 
occurrence of an oblique shallow constriction and sinuated lower border points to 
a byssiferous ancestor, and a probable line of descent from a Mytilus-like form. 
With regard to the question of eroded umbones in Carbonicola, some authors 
have described such a condition. The first was Professor Prestwich, whose note 
on the point I have quoted before.’ Goldfuss® stated that the umbones of his 
specimens were ‘‘abgeriebene,”’ though this word does not usually carry the 
meaning of erosion, but rather that of polish by friction. Ludwig’ also uses the 
term “mit abgeriebenem Wirbel,” but I could not make out that his specimens 
had been eroded anterior to fossilisation. Still a large number of specimens from 
the roof of the Cockshead Seam of North Staffordshire exhibit unimpeachable 
1 Op. supr. cit. 
2 «Handbuch der Palaeontologie,’ vol. 11, p. 61, 1881. 
3 ‘ Blemente der Palaeontologie,’ 1892, p. 265. 
+ ©Geol. Surv. Mem., Iron Ores of South Wales,’ pt. 3, pp. 226, 284, 236, 1861. 
D 1e5 5h, 6 « Petrefact. Germ.,’ p. 180 
7 *Palaeontograph.,’ 1859, Band viii, p. 38. 
