so CARBONIFEROUS LAMELLIBRANCHIATA. 



LiTHODOMUS CARBONARius, sp. nov. Plate II, fig. 14 — 19. 



Specific Characters. — Shell of moderate size, transversely ovate, lanceolate, 

 moderately convex, and somewhat oblique. The anterior end is narrow, very 

 small, with a bluntly rounded terminal border. The inferior border is gently 

 convex in its whole extent, and slightly oblique downwards and backwards. 

 Towards the posterior end it rises again, and forms a blunt curve with the posterior 

 border, the convexity being downwards and backwards ; above, the posterior 

 border is obliquely truncate, but becomes rounded below. The hinge-line is straight, 

 equal in length to about from three-quarters to two-thirds of the extreme length 

 of the shell. It joins the posterior border at a very obtuse angle. The umbones 

 are small a7id inconspicuous, hardly elevated above the hinge-line, very anterior, 

 but not terminal, marked off from the shell in front by a slight groove. The 

 valves are somewhat convexly swollen, more so above, and compressed and 

 slightly expanded upwards posteriorly. There is no ridge or keel. 



Interior. — The anterior adductor scar is excavated, marginal, and rounded. The 

 posterior has not yet been exposed. The hinge-line is simple, slightly thickened, and 

 edentulous ; bevelled at its lower edge for the insertion of an internal ligament. 



Exterior. — The surface is ornamented with irregular plicae and lines of growth 

 oblique to the long axis of the shell, and parallel with the borders. Shell thin, 

 covered with a periostracum. 



y-. . . Dorso-veutrally at 



UimenSlOnS .■ Antero-posteriorly. end of hinge-line. 



PI. II, fig. 16, from Randerstone, measures 25 mm. 9 mm. 



PI. II, fig. 17, from Bskdale ,, 20 mm. 8 mm. 



Localities. — Scotland, Limestone No. 5, Randerstone, Fife, Calciferous Sand- 

 stone series; Eskdale; " Scorpion-beds," Lower Carboniferous. 



Observations. — I know of no described fossil shells to which I can refer the 

 specimens obtained from Randerstone and Eskdale. Fortunately the slab from 

 the former locality has exposed on it two interiors, in which the hinge characters 

 have been observed. This is in the possession of Mr. J. Kirkby, of Leven, who 

 referred the shell to L. dactyloides, M'Coy, in his paper " On the Marine Fossils 

 in the Calciferous Sandstone series of Fife." ' Q. J. Geol. Soc ,' 1880, p. 578. 



The Randerstone shells have lost their outer coating and periostracum, and 

 appear smooth ; but the Eskdale specimens have this coating well preserved. 



In the majority of the shells from the latter locality both valves are in contact 

 but lying flat open, and united by the ligament on the planes of sedimentary 

 deposit, pointing to the death of the animal prior to the entombment of the shell. 

 Specimens in this condition are found of all sizes, from that of a pin's head to that 

 of the specimen whose measurements are given above. 



