322 BRITISH SILURIAN BRACHIOPODA. 



our plate. The differences between it and Leptana quinquecostata (M'Coy) are less 

 striking ; and we are not yet acquainted with the internal characters of the latter shell. 



Position and Locality. It occurs plentifully in the Wenlock Shale near Dudley, and 

 at Build was, near Wenlock, &c. 



Abroad it was found by Dr. Lindstrom in the Middle Gothland beds at Djupvik 

 (Eksta), and Lilla Carlso, Gothland. 



LEPT.ENA QUINQUECOSTATA, M'Coy. (sp.). PL XL VIII, figs. 23 — 27. 



Orthis quinquecostata, ilf'Coy. Sil. Foss. Ireland, p. 33, pi. iii, fig. 8, 1846. 

 Lept^na — Id. Brit. Pal. Foss. p. 236, 1852. 



— — Schmidt. Sil. Form. Ehstland ; Archiv, &c., p. 216, 1858, 



— — Salter. Siluria, 3rd ed., p. 211, fig. 3, 1859. 



— — D'Eickwald. Leth. Rossica, Per. Anc, vol. i, p. 872, 1859. 



— — Salter. Mem. Geol. Survey, vol. iii, p. 266, 1866. 



Sj^ec. Char. Semicircular, wider than long, greatest width at the long straight 

 hinge-line ; cardinal extremities rounded, sometimes slightly prolonged in the shape of 

 semicylindrical ears. Ventral valve convex, much arched in profile, and especially so at 

 the beak, flattened towards the sides ; beak small, incurved ; area triangular, moderately 

 wide ; fissure narrow, arched over by a convex pseudo-deltidium. Dorsal valve concave, 

 following the curves of the opposite valve ; area about one third of the width of that 

 of the other valve. Surface of both valves ornamented with three, five, or seven principal, 

 equidistant, slender, thread-like rounded radii, which extend from the beak to the margin, 

 leaving very wide interspaces, which are closely and finely striated longitudinally ; an 

 occasional shorter rib occupying the centre of the interspace, and extending a short way 

 from the margin in the direction of the beaks. Interior not well known. 

 Length 3, width 6, depth \ line. 



Ohs. This small species appears to bear much resemblance to Leptana segmentiim, 

 but is distinguished exteriorly by its smaller number of principal radii, which in most 

 specimens do not exceed five. Its beak is also larger and more projecting than in L. 

 segmentum. I have never been so fortunate as to be able to examine the interior of its 

 valves. Prof. M'Coy remarks that the internal cast of the ventral valve presents a very 

 short mesial septum, dividing the small, tumid, reniform pair of muscular impressions, 

 reaching only to one fifth of the length of the shell ; that from these, five or six slender, 

 branched impressions of the pallial vessels extend on each side to the margin, a broad 

 border round which is very minutely and closely punctured under the lens, the rest of 

 the cast being seemingly nearly smooth. Prof. M'Coy further observes that it is 

 internally easily distinguished from L. sericea by its extremely short muscular impressions, 



