208 CARBONIFEROUS LAMELLIBRANCHIATA. 



Nuculana acuta, Sowerby, sp., 1840. Plate XV, fig. 47, 47 a. 



Nucula acuta, Sowerhy, 1840. Trans. Greol. Soc, ser. 2, vol. v, Appendix, pi. 



xxxix, fig. 4. 



— — Morris, 1843. Cat. Brit. Foss., p. 93. 



— — — 1854. Ibid., 2nd edit., p. 216. 



Ctenodonta acuta, Bigsby, 1875. Thesaurus Devonico-Carboniferus, p. 305. 

 Nucula acuta, Etheridge, 1888. Brit. Foss., pt. 1, Palaeozoic, p. 287. 



Specific Characters. — Shell small, transversely ovate, acutely pointed behind. 

 The anterior end is shorter than the posterior, but is the deepest portion of the 

 shell in a dorso-ventral diameter, and its border is semicircularly curved. The 

 inferior border is curved, with its convexity downwards. The posterior border is 

 very short and pointed. The hinge-line is arched ; the two limbs (of which the 

 anterior is the shorter and less obliquely set, and the posterior the longer, 

 rapidly depressed) meet at an angle beneath the umbo. The umbones are small, 

 pointed, and incurved, raised and situated in front of the middle line of the shell. 

 The valves are evenly convex, with a slight angle on the posterior slope. 



Interior. — The arrangement of the muscle-scars and hinge appears to be 

 normal as observed in casts. 



Exterior. — The surface is adorned with regular concentric lines, most apparent 

 at the lower margin of the shell. 



Dimensions. — The type, PI. XV, fig. 47, measures — 



Antero-posteriorly . . . .5 mm. 



Dorso-ventrally . . . .3 mm. 



Locality. — The Pennystone Ironstone, Coalbrookdale. 



Observations. — I have been able to study only a single specimen of this species, 

 which 1 believe to be the type figured by Sowerby (op. cit.). It is preserved in 

 the British Museum (Nat. Hist.), and was acquired from the Collection of the late 

 Sir Joseph Prestwich. 



The specimen is very small. I am unable to identify any other shells with it, 

 and unfortunately there is at present not sufficient material to speak with any 

 certainty on the affinities of the species. I fear that, owing to the smallness of 

 the shell, few specimens will be preserved. 



In the original drawing the figure of a hinge-plate is also given (fig. 5 a). 



The original description is — " Transversely ovate, convex, concentrically 

 striated; anterior extremity rounded; posterior extremity produced, pointed. 

 Length 1^ lines, width 2\ lines." 



