PTERONITES ANGUSTATUS. 



Pteeonites ANGUSTATUS, M'Coij, 1844. Plate V, figs. 1 — -5. 



Pteronites ANGUSTATUS, M'Coij, 1844. Synops. Carb. Foss. Irelaud, ,p. 81, pi. 



xiii, fig. 6. 



— — Morris, 1854. Cat. Brit. Foss., 2ud edit., p. 181. 



— — Bi(jsby, 1878. Thesaurus Devonico-Carboniferus, p. 295. 



— XAYiFORMis, de Koninck, 1885. Ann. Mus. Eoy. Hist. Nat. Belg., 



torn, xi, p. 187, pi. XXX, fig. 26. 



— suBVENTRicosus, (h Koiiinck, 1885. Ibid., p. 186, pi. xxx, fig. 25. 



— ANGUSTATUS, Efherulge, 1888. Brit. Foss., pt. 1, Palaeozoic, p. 276. 



Specific Characters. — Shell small, very inequilateral, almost arciform, pointed 

 behind and compressed in front. Anterior end very small but distinct, 

 l)lunt. The lower border sweeps round from the antero-superior angle to the 

 postero- superior angle without a break ; l)ut the anterior half is a segment of a 

 greater circle than the posterior portion, and therefore appears flatter. The hinge- 

 line is straight, the greatest antero-posterior diameter of the valve. The umbones 

 are small, gibbose, slightly raised above the hinge-line, and placed very far forward 

 but not quite terminal. The anterior part of the valve is oljliquely swollen, 1)ut 

 posteriorly the valves are much compressed and expanded ; the posterior wing i.s 

 not marked off from the rest of the valve. The hinge edge is rolled and thickened, 

 marked off from the valve by an elongate narrow groove. 



Exterior. — The surface is ornamented with regnlar equidistant ridges parallel to 

 the margin, most marked over the oblique gibbosity, becoming almost obsolete 

 in front and behind. These ridges are separated by smooth flattened spaces. 

 Shell thin. 



Dimensions. — PI. V, fig. 1, a compressed .specimen from Lawston F^inns, 

 Liddle Water, measures — 



Antero-posteriorly . , . . o5 mm. 



Dorso-ventrally . . . .14 mm. 



Localities. — England : the Carbonaceous series of Lewisbm-n, Northumberland ; 

 above the masses of Limestone on Calcareous Shale, AVTiitewell, Yorkshire ; beds 

 above the Underset Limestone, Goodham Gill, Swarth Fell. Scotland : fjarriston 

 Burn, Archerbeck Burn, four miles north-west of Canonlne ; river Esk, north of 

 {xlencartholm, Dumfriesshire. Ireland : Arenaceous Shale, Bruckless, Dunkineely, 

 CO. Donegal. 



Obseriy-atioiis. — The specimen, PI. V, fig. -5, of Pferonifes angnsfatns in the 

 (xriffith Collection, ^Museum of Science and Art, Dublin, can, I think, hardly be the 

 type specimen. The figure given by M'Coy is so good that it seems to me possiljlo 



