514 BRITISH PALAZOZOIC FOSSILS. [LaMELLIBRANCHIATA. 
Genus. CARBONICOLA (M*Coy). 
Gen. Char.—Shell moderately elongate, ovate, thick; beaks moderate, not eroded; a strongly marked 
ovate lunette in front of the beaks; cartilage and ligament thick, external; periostraca thick ; surface usually 
coarsely imbricated concentrically. One very thick cardinal tooth in the right valve diverging obliquely 
towards the posterior side, one long anterior, and one long posterior lateral tooth; pallial scar entire; one 
moderate, oval, adductor impression at each end, each surmounted by a small accessory impression ; no lunate 
small impression below the anterior adductor as in Unio. 
From the time of Martin’s Petrefacta, and the first volume of Sowerby’s Mineral Conchology, many 
persons have strongly expressed their conviction that the bivalves occurring in such numbers as to form regular 
beds in the shale of our coal-fields, and in the accompanying ironstone and “ mussel-bind,” were truly con- 
generic with the recent Unios of our rivers. More recently certain shells of the lias and other marine strata 
of newer date, also called Unio by Sowerby, were erected into a genus under the name Pachyodon by Stuchbury, 
from an examination of the hinge; and he supposed, from the great similarity in external appearance 
between the so-called Unios of the lias and those of the coal, that the dental characters which he had dis- 
covered in the former existed in the latter, and that they belonged to one genus: this view was adopted by 
the describer of the greater number of these coal-shells, Capt. Brown, in his Memoir, in the Annals of Natural 
History for 1848. The name Pachyodon haying been preoccupied, was changed to Cardinia by Agassiz, who 
in his translation of Sowerby’s Mineral Conchology gives that generic title to both the marine oolitic, and the 
coal-measure fossils, and in this he has been followed by de Koninck and all the other palzontologists of note. 
Shortly after Agassiz proposed the name Cardinia, M. de Christol proposed that of Sinemuria (from Sinemurium, 
Sémur, Cote d’Or) for the same group, his typical species being of the ordinary lower oolitic marine type, or 
true Cardinia. Prof. Pronn and Prof. King are the only persons I know of who entertained the probability that 
the coal-shale fossils in question might be distinct from Cardinia ; the former in his Index Palwontologicus, re- 
placing them in Unio, and the latter having, in the Annals of Natural History for 1844, stated that he intended 
to use the word Axthracosia for a genus he intended establishing at some future time for the Unios of the 
coal-measures; this intention seems to have been given up, as the genus was never characterised, and neither of 
these authors seem to have possessed any knowledge of distinctive characters between these shells and 
Cardinia proper, except perhaps the difference of habitat. I have now however, after great trouble, succeeded 
in developing the internal characters of the present fossils, and find them distinguished from Unio by the large 
cardinal tooth diverging towards the posterior instead of towards the anterior end, by each of the adductors 
having one small accessory impression over it, without the lunate impression on the ventral margin of the 
anterior adductor of that genus, and the beaks not being eroded; from Cardinia it differs entirely in having the 
long lamellar lateral teeth of Unio, and wanting the thick remote conical lateral teeth of that genus. I only 
know this genus at present in the shales and ironstones of the coal-measures (where there are nearly twenty 
species), and associated exclusively with fresh water and terrestrial remains. The cardinal tooth separates the 
genus from Hdmondia, with which it might sometimes be confounded. 
CARBONICOLA ACUTA (Sow. Sp.) 
Ref. and Syn.= Unio acutus Sow. Min. Con, t. 33. f. 5 to 7. =U. aquilinus id. Geol. Trans. t. 39. f, 12. 
=Pachyodon lateralis Brown, An. Nat. Hist. Vol. XII. t. 15. f. 3.=P. exoletus id. ib. t. 16. f. 4. 
= P. antiquus id. ib. t. 16*. f. 4. = P. transversus id. ib. t. 16*. f. 5. =P. levedensis id. ib. t. 16*. f. 8. 
Desc.—Elongate, ovato-oblong; anterior side short, rounded; anterior lunette moderately small; 
beaks small, very obtuse, not prominent; valves tumid and very obtusely rounded close to the hinge-line; sides 
nearly flat, slightly convex: ventral margin nearly straight, very slightly convex near the anterior end; posterior 
end elongate, narrowed obliquely, subtruncate, rounded at the angles; surface marked with coarse, irregular, 
concentric strie of growth ; external cartilage prominent, about half the length of the hinge-line. Length one 
inch nine lines, in proportion thereto length of anterior end ;;,, greatest width from a little behind the beak to 
