PTEBINOPECTEN TESSELLATUS. 03 



genus, the ornament is practically the same on each, though its character is stronger 

 on the left and more eon vex valve. From /'. Hgidus, /'. meleagrinoides is dis- 

 tinguished by its smaller amount of obliquity, its tesselated ornament, and short 

 posterior side. 



Pteiunopeuten TESSELLATUS, Vh ill i ps, sp., 1836. Plate IX, figs. 8 — 11. 



Avicula tessellata, Phillips, 1836. Geol. Yorks., pt. ii, p. 211, pi. vi, fig. <i. 



— de Koninck, 1843. Desci - . Anim. Foss. Terr. Carb. Belg., 



p. 134, pi. vi, fig. 2. 

 Meleagrina tessellata, M'Coy, 1844. Synops. Carb. Foss. Ireland, p. 81. 

 Avicula tessellata, Brown, 1849. Illust. Foss. Couch., p. 102, pi. lxvi**, fig. 31. 

 Aviculopecten tessellatus, Morris, 1854. Cat. Brit. Foss., 2nd edit., p. 166. 



de Koninck (pars), 1885. Ann. Mus. Eoy. d'Hist. 

 Nat, Belg., torn, xi, p. 218, pi. xxxiii, figs. 33, 34. 



Specific Character*. — Shell small, somewhat semicircular, the left valve 

 moderately gibbose, the right flattened, inequilateral. The anterior and inferior 

 borders rounded, the posterior being broadly rounded below, slightly concave 

 above. The hinge-line long and straight. The umbones placed in front of the 

 middle line, the left one gibbose and slightly raised, pointed, the fight small, 

 flattened, and not raised. The anterior ear in the left valve well defined and 

 rolled, in the right valve long, severed from the valve by a long, deep slit for the 

 byssus. The posterior ears not well marked off from the valve, postero-superior 

 angle produced. 



Interior. — Unknown. 



Exterior. — The surface of the valve is ornamented by few widely separate 

 rounded ribs, slightly moniliform where crossed by lines of growth; rarely fine 

 secondary ribs arise in the flattened, smooth spaces between the primary ribs, 

 towards the lower margin. The ribs are crossed by well-marked, almost equi- 

 distant, concentric lines of growth, giving the valve a tesselated appearance, less 

 well marked on the ears than elsewhere. 



Dimensions. — A fairly perfect left valve, shown in PI. IX, fig. 11, measures — 

 Antero-posteriorly . . . .19 mm. 



Dorso-ventrally . . . 17 "5 mm. 



Elevation of valve . . . .4 mm. 



Localities. — England : the Carboniferous Limestone of Settle, and Shales above 

 the " massif," Whitewell, Yorkshire; Oastleton and Thorpe Cloud, Derbyshire'. 

 Ireland: Carboniferous Limestone of Little Island and Ballinabointra, co. Cork; 

 Ardshanbally, co. Limerick. 



