250 BRITISH SILURIAN BRACHIOPODA. 



Orthis porcata, MCoy. PJ. XXXI, figs. 12—20. PI. XLVI, fig. 4. 



Orthis grandis, Portlock (not of Sowerby). Report Geol. County of Londonderry, 

 &c., p. 4,52, p]. xxxii, fig. 25, 1843. 



— INFLATA, Saltei'. Quart. Joiirn. Geol. Soe., vol. i, table opposite p. 21, 1845. 



— POKCATA, M'Coy. Sil. Foss. Ireland, p. 32, pi. iii, fig. 14, 1846. 



— INFLATA, Salter. Mem. Geol. Survey, vol. ii, p. 372 ; and var. j3, retrorsa, p. 



373, pi. xxvii, figs. 3, 4, 1848. 



— PORCATA, M'Coy. Brit. Pal. Foss., p. 223, pi. i h, figs. 41, 42, 1852. 



— — Salter. Siluria, 2nd ed., p. 210, fig. 5, 1859. 



— Cakleyi, Hall. 13tli Rep. Reg. N. Y., p. 120, 1860. 



— PORCATA and 0. retrorsa, Billings. Geol. Survey of Canada, Pal. Ser.,vol. i, 



pp. 135, 136, 1862. 



— Anticostiensis, Shaler. Bull. Mus. Comp. Zool. Havard Coll., No. 4. 



— porcata, Billings. Cat. of Sil. Foss. of tlie Island of Anticosti, Can. Survey, 



p. 74, 1866. 



— — var. RETRORSA, Salter. Mem. Geol. Survey, vol. iii, p. 338, pi. xix, 



fig. 4, 1866. 



Spec. Char. Semicircular, semi-elliptical, or slightly subquadrate, a little wider than 

 long, broadest at half the length ; hinge-line straight, rather less than the greatest breadth 

 of shell ; cardinal extremities angular, sides and front rounded. Ventral valve either 

 almost flat or slightly convex at the beak and on the lateral portions, moderately depressed 

 or gently concave longitudinally along the middle, so as to produce a slightly convex curve 

 at the front margin ; area not very wide, with a triangular open fissure in the middle. 

 Dorsal valve evenly convex, but varying much in depth or gibbosity, the lateral portions 

 close to the hinge-line being flattened ; hinge-area rather narrow. Surface of valves 

 marked by very numerous small, strong, radiating ribs, from forty to about eighty in 

 number, with interspaces of about equal width, the ribs augmenting in number at a short 

 distance from the beaks, and especially so in the vicinity of the margin, by the interpolation 

 of one or two intermediary shorter ribs between the longer ones, the whole being crossed 

 at intervals by concentric lines of growth. In the interior of the ventral valve the 

 muscular area is remarkably square, and indented in front ; while in the dorsal valve the 

 cardinal process is small and placed between two deviating, moderately sized brachial 

 laminae, the oval muscular scars being separated by a rounded ridge. Three specimens 

 measured — 



Length 15, width 18, depth 8 lines. 



,, 15, „ 15 lines. 



., 16, „ 20 „ 

 Obs. The first British describer of this species seems to have been my distinguished 

 friend the late General Portlock, who, in his excellent ' Report on the Geology of London- 

 derry, Tyrone, and Permanagh,' published in 1843, described and figured our shell under 



