12 CARBONIFEROUS LAMELLIBRANCHIATA. 



Exterior. — The surface is ornamented with fine, close, concentric striae and 

 lines of growth, which follow the line of the posterior margin on the posterior ear, 

 and terminate in the hinge-line. 



Dime lis ions. — PI. II, fig. 7, the type of Phillips's Gervillia hinulata, measures — 

 Antero-posteriorly . . . .45 mm. 



Dorso-ventrally . . . .24 mm. 



From side to side (estimated) . . .10 mm. 



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

 Thorpe Cloud, Derbyshire ; Settle, Hill Bolton, Cracoe, and Withgill, Yorkshire ; 

 Clitheroe, Lancashire ; Poolvash, Isle of Man ; the Underset Limestone, Farcote 

 Gill and Goodham Gill, Swartli Fell. Scotland : the Upper Limestone series of 

 Howrat, Dairy ; Hurlet series, Maol Doun, Bute ; Knockhill Quarry, Strathkiness, 

 Fife. Ireland : the Carboniferous Limestone series of Millicent, Clane, co. Kildare ; 

 Doohyle, co. Limerick; Ballybriggan, co. Kerry; and Park Adelear, co. Cork. 



Observations. — Fortunately the type of Phillips's Gervillia lunulata is preserved 

 in the Gilbertson Collection, Natural History Museum, South Kensington, and I 

 am permitted to refigure it by the kindness of the authorities, PI. II, tig. 7. The 

 specimen is a little imperfect in front, l)ut otherwise is very well preserved. 



I think Avicula recta, M'Coy, refigured PI. II, fig. 8, and A. laevigata, PI. II, fig. 

 11, represent the very young and adult forms of Pliillips's species. The specimens 

 are in the Grifiitli Collection of the Museum of Science and Art, Dublin, and the 

 authorities have kindly permitted me to reproduce the specimens. The important 

 characters which distinguish 1j. luvnlnta from other species of the genus are the 

 peculiar shape, and tlie narrowed, almost pointed postero-inferior angle, the 

 strongly marked-off posterior wing, and the acutely rounded, curved edge to the 

 posterior slope. 



L. hirundo, de Koninck, is more triangular and transverse, less oblique, and 

 has a much longer process to the hinge-line posteriorly. It will be noted in 

 L. lunulata that this process does not extend very far beyond the margin of the 

 shell. 



L. lunulata was well and fully described by M'Coy (op. supra cit.) undei' the 

 generic name Pterinea. In remarks on the species 1\ laevigata he says, " This fine 

 shell bears some resemblance to (rervillia lunulata of Phillips, but is easily 

 distinguished by its greater size, wider posterior end, smooth surface, and the total 

 absence of the steep posterior ridge, which in that species separates the posterior 

 ear from the body of the shell." In the original specimen, PL II, fig. 11, this ridge 

 is seen to be present and well marked. It is possible, therefore, that the types 

 which served for the second description, said to come from Derbyshire, may have 

 belonged to L.grandis, PI. Ill, figs. 12 — 15. The smoothness of the surface depends 

 largely on the preservation of the fossil and the wideness of the posterior end 



