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 Garbonicola, 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 Garbonicola 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 Garbonicola differs from modern 

 Unionidse 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 : — 1st, 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 Garbonicola 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 Garbonicola 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 Garbonicola 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 at a 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 



