CARBONICOLA. 39 
Surface marked with coarse concentric lines of growth. Periostracum thick, 
often wrinkled. Ligament external. Shell closed all round, nacreous, with 
occasionally pearly nodules. Radiating lines. 
Interior :—Pallial line simple. Anterior-adductor scar large, almost marginal. 
Posterior-adductor scar large. Scars of the anterior-pedal muscles are situated 
above and slightly behind the anterior-adductor impressions. 
Hinge-plate triangular, thickened, variable, with or without cardinal teeth. 
No anterior or posterior lateral teeth. 
Observations.—Much uncertainty has existed amongst previous observers as 
to the true generic character of Carbonicola, and this doubtless arose from the 
paucity of specimens showing the hinge-structure, and the very variable appear- 
ance of the specific forms. The general consensus of opinion has, however, been 
that Carbonicola possessed marked Unioniform characters, and that in them we 
have some of the oldest representatives of this family. The chief facts in support 
of this view are the association of these fossils with plant and reptilian remains, 
and the anatomical features of the shells. The more important of these are—the 
shell being composed of an internal or nacreous layer, and an outer or prismatic ; 
the thickened and wrinkled periostracum ; occasional erosion of the umbones ; 
the plan of the hinge, though it differs much in detail from that of most Unios ; 
the simple pallial line, and the arrangement of the anterior and posterior adductor 
scars ; the frequent possession of an oblique shallow depression, commencing at 
the umbo and stretching backwards and downwards to the lower border; also the 
general shape of the shell. The points in which Carbonicola differs from modern 
Unionide are the position of the accessory-pedal scars ; the frequent non-erosion 
of the umbones; and the great variation of the hinge-structure in the species. 
I have been compelled to drop Prof. King’s name of <Anthracosia for two 
reasons :—Ist, that in his original publication (‘ Ann. Mag. Nat. Hist.,’ vol. xiv, 
1844, p. 313) no description or figure of the characteristic features was given ; 
2nd, that although M‘Coy’s name of Carbonicola is accompanied by a partially 
erroneous diagnosis, and unaccompanied by figures, yet there is no doubt whatever 
as to what shells are described under this name; neither is there any question 
as to priority, the publication by M‘Coy of the name Carbonicola was at once 
commented on by King in a letter which I have quoted antea, p. 21. 
The form of hinge described by Professor King is not, however, typically 
characteristic of the genus, but is that form which obtains only, as far as I am yet 
aware, in Carbonicola aquilina. Unfortunately the original specimens are not to 
be found, unless a very fragmentary example showing the hinge, in the Museum 
of Newcastle-on-Tyne, labelled in King’s handwriting, is one of them. 
I am ata loss to account for the description of the hinge as given by Professor 
M‘Coy (‘ Brit. Pal. Foss.,’ p. 514), where he says that it consists of “ one very 
