432 CARBONIFEROUS LAMELLTBRANCHIATA. 



Tbllinomorpha jucunda, de Koiiitichy sp., 1885. Plate XLIX, fig. 4. 



Ch^nomta jucunda, de Koninnk, 1885. Ann. Mus. Koy. Hist. Nat. Beige, 



vol. xi, p. 7, pi. i, figs. 1—8 ; pi. xiii, figs. 38, 39. 



Specific Characters. — Shell above the medium size, transver.sely ovate, tumid, 

 gaping posteriorly, without a keel, very inequilateral. The anterior end is short, 

 blunt, turgid, depressed ; its margin bluntly rounded, but salient. The 

 inferior border is almost straight, and may be concave about the junction of the 

 anterioi and middle thirds of its extent ; it becomes more convex behind. The 

 posterior end is truncate above, but bluntly rounded below, its superior and 

 inferior angles being almost obsolete ; the posterior border is about as long as any 

 dorso-ventral diameter of the valve. 



The hinge-line is arched in front, but almost straight behind, much shorter 

 than the shell, and depressed. The umbones are small, depressed, incurved, and 

 not contiguous, placed in the anterior third of the valve. The lunule is small 

 and shallow ; the escutcheon long and shallow, but very broad, bounded 

 externally by an erect, low, bluntly angular ridge, which passes backwards from 

 the umbo to the posterior border, and internally by the erect hinge-line. 



The valves are regularly convex from above downwards, but the antero- 

 posterior curvature is interrupted by a broad, well-marked shallow sinus, which 

 extends from the umbo to the inferior margin, at the junction of the anterior aud 

 middle thirds of the valve. The dorsal slope is only slightly compressed. 



Interior. — The anterior adductor muscle-scar is almost obsolete, with no ridge 

 behind it ; the posterior scar is normal in position ; the pallial line entire. The 

 hinge-plate is much thickened below the umbones, but the actual hinge has not 

 been isolated. 



Exterior. — The surface is ornamented with irregular folds and wrinkles, con- 

 centrically arranged, and fine strice and lines of growth. There is obscure 

 evidence that the surface was covered with radiating rows of granules or 

 tubercles. Shell thiu. 



Bimensions. — Owing to the fact that I have not been able to examine any 



perfect British examples of this species, I give the dimensions of a Belgian 



specimen from the Carboniferous Limestone of Tournai, which measures — 



Antero-posteriorly . . . .87 mm. 



Dorso-ventrally . . . .48 mm. 



From side to side . . . .41 mm. 



Localities. — England : the Carboniferous Limestone of Park Hill,. Derbyshire. 

 Ireland : Rathkeale, co. Limerick. 



