216 BRITISH SILURIAN BRACHIOPODA. 
Spec. Char. Shell nearly orbicular or rotundato-quadrate, wider than long, greatest 
width anteriorly ; hinge-line straight, a little less than the width of the shell. Ventral 
valve very moderately and uniformly convex ; beak small, area about one seventh as wide 
as long. Dorsal valve very gently convex, with a shallow longitudinal mesial depression 
along the middle, widest towards the front; hinge-area linear; surface of both valves 
covered with numerous thread-like radiating strie, which increase in number at various 
distances from the beaks by the interpolation of shorter ribs. In the interior of the 
dorsal valve a small cardinal process is situated between two slightly projecting brachial 
processes or plates, which, however, extend along the bottom of the valve to some little 
distance along the posterior half of the muscular disc; a small central ridge proceeds 
likewise from the base of the cardinal process to about one third of the length of the valve, 
while on either side is situated an elongated muscular area, laterally margined by a slightly 
projecting ridge. In the interior of the ventral valve there exists a moderately sized 
saucer-shaped muscular depression, surrounded by a raised margin, while along the 
middle is situated a small pear-shaped scar, due to the occlusor or adductor muscle. In 
the internal casts the hollows above described are represented by corresponding 
elevations, Wc. 
Length 4, width 6, depth 2 lines. 
Obs. As justly remarked by Prof. M‘Coy, the great depression and near equality of 
the valves, much finer strize, and singular elongated narrow form of the elongated muscular 
impressions, and, I might add, prolongation of the brachial processes or lamellz in the 
posterior portion of the muscular disc, easily distinguish this species from O. dasalis and 
some other nearly allied forms. ‘This last-named feature is well seen in the internal cast 
fig. 3, and in the enlarged view of the interior of the same valve fig. 3, a. 
Position and Locality. This species occurs abundantly in the Upper Ludlow at 
Whitecliff, and in several other localities near Ludlow in Shropshire ; at Wonder, Wool- 
hope, &c. Messrs. Phillips and Salter record its presence in rocks of a similar age in 
various localities in the Malvern, Abberley, Woolhope, Usk, Builth, and Llandeilo districts. 
It does not yet seem to have been found in Scotland, and I am not really certain whether 
it really occurs in Ireland, although General Portlock mentions it from Desertcreight, 
Tyrone, with a mark of doubt. 
Orrnis GIRVANIENSIS, sp. nov. Pl. XXVIII, fig. 10. 
Spee. Char. Almost circular, about as wide as long, both valves very convex, without 
fold or sinus, the dorsal one at times almost gibbous; hinge-line slightly exceeding half 
the width of the shell, slightly truncated in front. In the ventral valve the beak is 
angular, the area small, triangular, with open fissure. In the dorsal valve it assumes a 
