CARDIOMORPHA OBLIQUA. 263 



any certainty on the value of this " species," which may turn out to be only a 

 variety of G. oblong a. 



Cardiomorpha obliqua, Hind, sp. nov. Plate XXIV, figs. 3 — 5, 5 a, 5 b. 



Specific Characters. — Shell ovate, inequilateral, obliquely gibbose. The 

 anterior end is short and narrow, but projects forwards in front of the umbones, 

 forming a rapidly compressed lobe with an elliptically rounded erect border, 

 passing gradually into the ventral margin, which is markedly convex and 

 extended, being much longer than the upper border. The posterior border is 

 bluntly but regularly curved, and about twice as extensive as the anterior, the 

 postero-inferior and postero-superior angles being gradually rounded. The 

 hinge-line is arched and somewhat extended, and depressed posteriorly. The 

 umbones are, in the anterior part of the shell, gibbose, large, not elongated, 

 elevated, twisted forwards and inwards, the apices being rolled on themselves. 

 The valves are obliquely swollen, the line of greatest convexity passing from the 

 centre of the umbones downwards to the middle of the inferior border. Both in 

 front of and behind this line the valves are rapidly compressed, especially poste- 

 riorly and upwards. The upper part of the anterior part of the valve is so much 

 excavated and compressed below the prosogyrous umbones as to be concave. 

 No lunule, but a well-marked escutcheon, which becomes broader and shallower 

 as it passes backwards. 



Interior. — The posterior adductor scar is large and round, situated near the 

 dorsal border in the hollow of the posterior slope, but remote from the posterior 

 end ; pallial line faint but entire. Hinge not exposed. 



Exterior. — The surface is almost smooth, but is seen to be covered with faint 

 concentric lines, collected into bands by very shallow grooves. Shell thin. 



Dimensions. — PL XXIV, fig. 3, from Ardlaman, co. Limerick, in the collec- 

 tion of the Geological Survey of Ireland, measures antero-posteriorly 50 mm., 

 dorso-ventrally 40 mm., from side to side 36 mm. 



Localities. — The Carboniferous Limestone of the Isle of Man. Ireland : the 

 Carboniferous Limestone of Ardlaman, co. Limerick. 



Observations. — This species is more regularly ovate than any other; more 

 transverse than G. orbicularis, and not oblong-quadrangular like G. oblonga. It 

 differs from both these species in possessing a prominent anterior end. The 

 peculiar oblique gibbosity and more erect elevated umbones also serve to imme- 

 diately distinguish it from the latter species. In adult specimens the posterior 

 end becomes more and more contracted by the approach of the upper and lower 

 borders. This is well shown in PL XXIV, fig. 4. 



