252 BRITISH SILURIAN BRACHIOPODA. 



sliire ; south of Llangollen, Cyrn-y-brain near Wrexham, and Glyn Ceiriog, Denbighshire ; 

 Llanfyllin, Meifod, Llanwddyn, Welshpool, Montgomeryshire ; near Corwen, Merioneth- 

 shire. Prof. M'Coy quotes it from the Bala schists of Llansaintfraid, Denbighshire, at 

 Meifod, and many other places, but it appears most abundant in the Coniston Lime- 

 stone at Coniston, from which locality a fine series of specimens may be seen both in the 

 Museum of Practical Geology and in Mr. Sharpens collection in the Museum of 

 the Geological Society. It has been likewise collected at Tan-y-Graig, in the Builtli 

 district ; at Bird's Hall and Myddleton Hall in the Llandeilo district, &c. 



In Ireland it was found for the first time by General Portlock at Tyrone, Desertcreat, 

 and by M'Coy at Portraine, Malahide, County Dublin ; also at Carrickadaggan, County 

 Wexford.^ 



Abroad, 0. porcata occurs in the shales of the Hudson-river group near Cincinnati ; 

 in the Trenton Limestone at Ottawa ; also at Anticosti, &c. 



Orthis Actoni^, Sow. PL XXXVI, figs. 5—17. 



OiiTHis AcTONLE, J. de C. Soiv. Sil. Syst., p. 639, pi. xx, fig. 16, 1839. 



— — M'Coy. Synop. Sil. Foss. Ireland, p. 28, 1846. 



— ■ — Phillips and Salter. Mem. Geol. Survey, vol. ii, p. 286, 1848. 



— — M'Coy. Brit. Pal. Fossils, p. 213, 1852. 



— — Salter. Mem. Geol. Survey, vol. iii, p. 339, pi. xxi, figs. 1, 8, 1866. 



— — /(/. Siluria, 4th ed., p. 192, fig. 2, and pi. v, fig. 11, 1867. 



Spec. Char. Semicircular, wider than long, the hinge-line being the broadest part 

 of the shell ; cardinal extremities extending into short mucronate wings ; front and sides 

 rounded. Ventral valve evenly convex, without sinus, flattened at the ears; area 

 narrow, foramen open, beak small, incurved. Dorsal valve flat or slightly concave, 

 especially at the umbone, and flattened at the sides or in the proximity of the cardinal 

 angles ; hinge-area very narrow. External surface of both valves ornamented with a 

 variable number of strong angular ribs, which increase in number from about the middle 

 of the margin by the general or occasional interpolation of one or two smaller ribs between 

 each pair of the larger ones. When young and up to a certain age the ribs are simple 

 and comparatively few in number, with wide interspaces between them, and the surface is 

 also covered by fine concentric lines. In the interior of the ventral valve a prominent 

 hinge-tooth exists on each side of the fissure, and is supported by short dental plates, 

 which partly enclose a moderately sized saucer-shaped muscular depression with raised 



^ Carrickadaggan is a famous fossil locality, especially for Echinosphcerites aiirantium, but is an obscure 

 spot, and the above is the name of the townland. It is south of the road from New Ross to Taghmou, 

 being about six miles south from the former place. 



