44 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



and writes of them as " maritime Unionidee ;" 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 Garbonicola is very different from that which 

 obtains in Cardinia. In Garbonicola 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 

 Cardinia is totally different from that of Carbonicola, and is described by 

 Woodward 1 as " cardinal teeth, obscure, laterals 1 — 0, — 1, remote, prominent." 

 Zittel, 2 Steinmann, and Doderlein 3 still retain Anthracosia as a sub-genus of 

 Cardinia. Salter 4 hazarded the view that Anthracosia {Carbonicola) might be 

 allied to the Mijadsd. 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 Myadge have, and no eroded beaks as is common in Unio ; but the 

 pallial 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 Carbonicola 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. 5 Goldfuss 6 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 7 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. ii, p. 61, 1881. 



3 ' Elemente der Palaeontologie,' 1892, p. 265. 



* ' G-eol. Surv. Mem., Iron Ores of South Wales,' pt. 3, pp. 226, 234, 236, 1861. 

 5 P. 5. 6 ' Petrefact. Germ.,' p. 180. 



7 'Palaeontograph.,' 1859, Band viii, p. 33. 



