236 BRITISH SILURIAN BRACHIOPODA. 
Orruis 1nTERCoSTATA, Portlock. Pl. XXXVIII, figs. 1—3. 
OrTHIs INTERCosTATA, Portlock. Report on the Geology of the County of Londonderry, 
&e., p. 454, pl. xxxvii, fig. 3, 1843. 
—_— — M‘Coy. Synopsis Sil. Foss. Ireland, p. 31, 1846. 
— — Salter. Siluria, 2nd ed., p. 543, 1859. 
Spec. Char. Nearly semicircular, a little wider than long ; hinge-line slightly shorter 
than width of shell. Ventral valve very moderately and uniformly convex; area narrow 
and small. Dorsal valve and interior not known. Surface marked by fine thread-like, 
longitudinal, radiating strie, with wide interspaces between each pair, in the centre of 
which is situated a smaller rib, which, commencing at various distances from the beak, 
extends to the front. 
Length 7, width 8 lines. 
Obs. Of this species only three or four ventral valves have come under my notice, 
notwithstanding that Prof. M‘Coy states it to be not uncommon in the sandy slates 
(Caradoc) of Bardahessiagh, Pomeroy, County Tyrone, as well as in the sandstone of 
Kaulley, Pomeroy, County Tyrone. Portlock mentions Desertcreat, Tyrone, as the locality 
from whence his specimen was derived. More material in connection with this species 
should be sought for. 
Orruis vesPertiLio, J. de C. Sow. Pl. XXX, figs. 11] —21. 
Ortuis BILOBATA, J.de CO. Sow. Silurian System, pl. xix, fig. 7, 1839. 
— VESPERTILIO, Jd. ibs pl. xx,.fie, lil; 
— . BILOBATA et VESPERTILIO, Portlock. Geol. Rep. of the County of London- 
derry, &c., p. 453 and table, 1843. 
—  VESPERTILIO, M‘Coy. Synopsis Sil. Foss. Ireland, p. 36, 1846. 
— — including O. BrLoBATa, Phillips and Salter. Mem. Geol. Survey, 
vol. ii, p. 291, 1848. 
— a M‘Coy. Brit. Pal. Foss., p. 230, 1852. 
— — F. Schmidt. Sil. Form. von Ehstland, &c.; Archiv Nat. Liv.-Ehst.- 
und Kurlands, vol. ii, p. 214, 1858. 
— — Salter. Siluria, 2nd edit., p. 74, fig. 7; and pl. vi, figs. 
1—3, 1859. 
Spec. Char. Rotundato-quadrate, greatest breadth usually at the hinge-line, some- 
times near the middle of the shell; sides slightly concave prior to being rounded at their 
cardinal extremities. In some individuals these extremities form small mucronate wings 
or angular prolongations; front indented by a concave curve. Dorsal valve convex, 
longitudinally divided into two lobes by a deep, obtusely angular median sinus ; the lateral 
