KLMICUOTIS IIEMISPILEIUCUS. 45 



Etjmiceotis hemisph^eicus, Phillips, sp., 1836. Plato VII, figs. 1—0. 



Pecten hemisph^ericus, Phillips, 1836. Geol. Yorks., pt. ii, p. 212, pi. vi, fig. 16. 

 Posidonomya hemisph^erica, de KonincJc, 1843. Descr. Anim. Fuss. 13elg., p. 142, 



pi. i, fig. 16. 

 Avicula. hemisphjerica, Brown, 1849. Illust. Foss. Conch., p. 160, pi. lxv, fig. 5. 

 Aviculopecten hemisph;ericus, Morris, 1854. Cat. Brit. Foss., 2nd edit., p. 164. 

 Rutotia hemisph^rica, de Koninck, 1885. Ann. Mus. Roy. d'Hist. Nat. Belg., 



torn, xi, p. 197, pi. xxxix, figs. 6, 7. 

 Cf. Streblopteria pr^lineata, de Koninck, 1885. Ibid., p. 204, pi. xxxii, fig. 4. 



Specific Characters. — Shell of medium size, suborbicular, a little inequilateral, 

 very inequivalve, the right valve only slightly convex, the left gibbose. The 

 anterior inferior margin convex, the posterior almost straight and nearly vertical. 

 The hinge-line straight, the smallest, antero-posterior diameter of the valve, 

 making well-marked right angles with the anterior and posterior margins. The 

 umbones subcentral, that of the right valve being small and not elevated, the left 

 being gibbose, elevated, and arched over that of the right valve. No posterior 

 ears, but the valves compressed at the antero- and postero-superior angles, 

 especially the latter, which is the larger and more pronounced. The right valve 

 deeply marked by a triangular pit, which runs up almost to the umbo, for the 

 byssus, and marks off a small ear from the rest of the valve ; left not cut, but 

 showing a more or less well-marked depression forming a swollen lobe in the 

 position of the anterior ear. Both valves more convex in the anterior than in the 

 posterior portion. 



Interior. — Details not observed. 



Exterior. — The surface is marked with very fine microscopic lines of growth, 

 sometimes squamous, best seen in the upper part of the valve, but to the naked eye 

 it is almost smooth. 



Dimensions.— PI. VII, fig. 1, a bivalved example from Hill Bolton, measures — 

 Antero-posteriorly . . . . 37 mm. 



Dorso-ventrally . . . .42 mm. 



From side to side . . . .18 mm. 



Localities. — England : the upper beds of the Carboniferous Limestone of 

 Castleton, Derbyshire; Settle, Hill Bolton, Yorkshire ; Narrowdale, Staffordshire; 

 and Poolvash, Isle of Man. Ireland: the Carboniferous Limestone of Little 

 Island, co. Cork; Clogherbrian, co. Kerry. 



Observations. — The type of Phillips's Pecten hemisphsericus is fortunately pre- 

 served in the Gilbertson Collection at the Natural History Museum. South 



