238 BRITISH SILURIAN BRACHIOPODA. 
Orruis rustica, J. de C. Sow. Pl. XXXIV, figs. 183—17; var. rigida, figs. 18, 19; 
var. Wallsalhiensis, figs. 20—22. 
OrtuHis RusTICA, J. de C. Sow. Silurian System, pl. xii, fig. 9, 1839. 
— —  M‘Coy. Synopsis Sil. Foss. Ireland, p. 34, 1846. 
— — Dav. London Geol. Journal, p. 64, pl. xiii, figs. 1—4, 1847. 
— riema, Id.  Ib., p. 63, pl. xiii, figs. 16, 17, 1847. 
—  kRusTIcA et var. RIGIDA, Dav. Bull. Soc. Géol. Fr., 2nd ser., vol. v, p. 322, 
pl. i, fig. 15, 1848. 
— Watsattti, Id. Ib., p. 339, pl. iv, fig. 7, 1848. 
—  CALLIGRAMMA, var. RUSTICA, Phillips and Salter. Memoirs Geol. Survey, 
vol. 11, p. 376, 1848. 
—— var. RIGIDA, Id. Ib., p. 376. 
— — » WatsaLLiensis, Id. Ib., p.376. 
— RUSTICA et var. RIGIDA, D’Orb. Prodrome, vol. i, p. 36, 1849. 
—  Ositensis, Schrenk. Schmidt’s Sil. Form. von Ehstland, &c.; Arebiv Nat. 
Liv.- Ehst.- und Kurlands, vol. ii, p. 213, 1858. 
—_— rustica, Salter. Siluria, 2nd ed., p. 544, pl. xx, fig. 10, 1859. 
_ rustica et O. RigiDA, W‘Coy. Brit. Pal. Foss., p. 226, 1852. 
— Rustica, Lindstrém. Gotlands Brachiopoder, p. 370, 1860. 
_ CALLIGRAMMA, Var. RUSTICA et RIGIDA, Salter. Mem. Geol. Survey, vol. iii, 
p- 337, 1866. 
_ — var. WALSALLIENSIS?, Id. Ib., (not O. Walsalliensis, Dav.) 
Spec. Char. Somewhat yotundato-quadrate or semicircular, broadest about the 
middle; hinge-line straight, slightly less than the width of the shell; sides rounded ; 
cardinal extremities sometimes rounded, more often angular from the lateral portions of 
the valves becoming slightly concave as they near the extremities of the hinge-line; front 
slightly indented. Darsal valve more or less convex, with sometimes a shght median 
longitudinal depression, but the front usually presents a small elevated curve; area well 
defined, but not quite as wide as that of the other valve. Ventral valve not so deep as 
the dorsal one, most convex at the beak, slightly depressed longitudinally towards the 
front; area triangular, of moderate width, fissure large and open; beak very small, scarcely 
produced beyond the apex of the area. Surface of valves covered with from fifty to one 
hundred and twenty small rounded ribs, of which two fifths or more are shorter than the 
others and interpolated between those that extend uninterruptedly from the beak to the 
margin. ‘The surface of valves are also concentrically crossed by small equidistant raised 
lines or ridges. In the interior of the dorsal valve, between two widely deviating brachial 
laminee, is situated a projecting cardinal process or boss, which is divided by a small 
longitudinal slit at its summit, while the posterior portion is narrow, the anterior is 
thickened. Under the cardinal process a short rounded ridge separates the small oval 
concave dendritic muscular scar. In the interior of the ventral valve, on either side of the 
x 
