100 CARBONICOLA, ANTHRACOMYA, AND NAIAD1TES. 



posteriorly, rather shorter than the length of the shell. The umbones are small, 

 contiguous, very slightly raised above the hinge-line, and situated at rather less 

 than oue third the length of the hinge-line from the anterior end. The lunule is 

 narrow and elongated. 



A broad obtuse gibbosity passes from the umbones diagonally across the shell 

 towards the posterior inferior angle, but becomes lost on the surface before 

 reaching that point. Anterior to the swelling is a shallow oblique sulcus, which 

 becomes very broad at the inferior margin, and corresponding in position to the 

 sinuosity. The superior and inferior borders are subparallel in medium-sized 

 and small specimens. The greatest dorso-ventral measurement is at or only 

 slightly in front of the posterior end. 



Interior. — Normal. The anterior adductor scar is shallow and marginal, the 

 accessory pedal scar punctiform in the usual situation. The posterior adductor scar 

 is rarely seen, owing to its shallowness and want of definition as to its margin. 



The surface of casts is marked by broad shallow sulci and fine radiating lines 

 at the anterior end and on the posterior slope. There is an elongate groove in 

 casts on either side of the line which marks the union of the valves posteriorly 

 for a short distance to receive the edge of the shell, which is there expanded 

 downwards at a right angle to itself to form the hinge-plate. 



Exterior. — The surface is almost smooth, covered with very fine concentric 

 lines of growth, which, crowded at their origin in front, become parallel to the 

 inferior border as they pass across the shell till they reach the diagonal swelling, 

 when they become reflected upwards at a rounded right angle towards the superior 

 border. The shell is very thin and seldom preserved. 

 Dimensions. — Fig. 12, PI. XIV, measures — 



Antero-posteriorly . . . .35 mm. 



Dorso-ventrally . . . .17 mm. 



Laterally . . . . .5 mm. 



Localities. — The roof of the Hard Mine Coal, North Staffordshire. Alldene 

 Colliery, Gateshead. Brown's specimen is said to have come from Wakefield. 

 High up in the Gannister series of Burrs, half a mile north of Bury, Bolton. 

 South Wales. Mine over the Three-quarter coal, Ebbw Vale. Eastfield, Upper 

 Coal-measures, Scotland. Ireland : Four-foot bed of shale over Coal III (Three- 

 feel or Old Colliery coal), Bilboa and Castlecomer. 



Observations. — I find in Captain Brown's ' Fossil Conchology ' (op. supra fit.) a 

 shell, which closely resembles in form those under description, under the name 

 Modiola Williamso?ii. He refers it to Modiola elongata, Williamson, MS., but 

 'j'lvrs no reason for the change of name. I unfortunately chose the latter name in 

 preference to that of Williamsoni in my paper on Anthracomya {op. supra cit.), 

 and have now to discard it in favour of the former, because the name A. elongata 



