224 BRITISH SILURIAN BRACHIOPODA. 
at its anterior extremity. The raised margin which surrounds the muscular cavity is con- 
tinued to within a short distance of the front in the shape of a narrow mesial ridge, while 
a broad parallel vascular trunk follows on either side the outer margin of the muscular 
cavity as well as of the mesial ridge, where, turning outwards and backwards, it encloses 
wide ovarian spaces. In the interior of the dorsal valve a large wide fissure encloses a 
concave cavity, longitudinally divided along the middle by a narrow mesial ridge; the 
brachial processes are very small, while a convex mesial longitudinal ridge separates into 
two pairs the quadruple impression formed by the adductor or occlusor muscle; the 
upper or posterior pair are transversely oval, while the anterior pair are obliquely placed, 
and deeply indented or forked laterally. 
Length 12, depth 13 lines. 
Obs. This isa very distinctive and singularly marked species. Externally it is finely 
striated, as in O. reversa, but is especially remarkable on account of the shape of its 
muscular impressions in the dorsal valve, and in the absence of a promiment cardinal process, 
as well as by the smallness of its brachial processes. It has hitherto been found only in 
the condition of internal casts and impressions. 
Position and Locality. O. Bailyana occurs at the Townland of Ballybro, one mile 
north of Tagoate, County of Wexford, in Ireland, the rock being a coarse grit of the 
Caradoc or Bala age (?). Together with it O. cal/igramma occurs in pleuty, as well as O. 
biforata, Leptena sericea, and Favosites fibrosus. 
I have named it in honour of Mr. W. H. Baily, Paleontologist to the Geological 
Survey of Ireland, to whom science is indebted for several valuable discoveries. 
Orruis REDUX, Barrande. Pl. XXVIII, figs. 6—9. 
OrtHIs REDUX, Barr. Silurische Brachiopoden aus Bohmen ; Naturw. Abhandl., vol. ii, 
p. 49, pl. xviii, fig. 7, 1848. 
— — Salter. Quarterly Journal Geol. Soc., vol. xx, p. 294, pl. xvii, fig. 7, 
1863. 
Spec. Char. Almost circular, slightly wider than long ; hinge-line less than the width 
of shell; ventral valve very moderately and uniformly convex ; beak small, area narrow. 
Dorsal valve almost flat, with a longitudinal depression along the middle, and small well- 
defined hinge-area ; surface of both valves closely covered with numerous thread-like 
striae, which increase in number towards the margin from the interpolation of one or 
two smaller striae between each of the principal ribs. In the interior of the ventral valve 
the muscular area is large and margined by a gently prominent ridge. In the interior of 
the dorsal valve the cardinal process is moderately large, and situated at the posterior 
extremity of a rounded ridge, which extends to nearly half the length of the valve, 
