64 BRITISH SILURIAN BRACHIOPODA. 
length from the posterior margin. Surface marked with small interrupted, more or less 
close, concentric ridges, separated from each other by interspaces of greater or smaller 
breadth ; lower or attached valve depressed, slightly convex near its apex, the oval fissure 
or perforation extending from near the centre of the valve to a short distance from the 
posterior margin. Surface as in the free valve, but a little more regularly marked. 
Three specimens measured— 
Length 9, breadth 9 lines. 
pi) a aka 
i (ales a Dine 
Oés. In external shape Discina perrugata seems to me to agree closely with Discina 
rugata ; and it is evident that the eminent Irish paleontologist has given the description 
from the sizgle specimen he has represented, for (as may be seen from the figures in our 
plate) both it and D. rugata present the same dimensions and shapes, as well as 
distances of the apex from the margin; but as Mr. Salter considers them distinct on 
account of a difference in the concentric striation, which he regards as being regularly 
wrinkled in D. perrugata, M‘Coy, and not like that of D. rugata, Sow., I have provision- 
ally kept them under distinct heads. ‘The shell-substance of D. rugata is distinctly 
corneous, and not punctured, as erroneously supposed by D’Orbigny. 
In Pl. [V will be found typical figures of Discina rugata, Sow., as well as of 
D. perrugata. 
Position and Locality. Sowerby, in Murchison’s ‘ Silurian System,’ enumerates the 
following localities for his D. rugata: 
“ Ludlow promontory, viz., Richard’s Castle; Bradnor Hill, Kington; Bagbarrow 
Hill; Pain’s Castle, Radnorshire, very abundant :” all in the Upper Ludlow rock. 
Phillips furnishes the following distribution, from the Upper Ludlow and Aymestry 
rock : 
Malvern district—Overley, Hale’s End, Mathon Coomb, Frith Hall Court; Upper 
Ludlow rock. 
Abberley district.—Ankerdine Hill, Aymestry limestone; Barrell Hill, Hole Farm, 
Wallgrove, Hillside Farm ; Upper Ludlow rock. 
Woolhope district.—Welsh Court, Shucknall Farm, Shucknall Hill, The Wonder, 
Old Sutton, Perton, &c., north-east of Pilliard’s Barn, Bodenham; Upper Ludlow rock, 
and Aymestry limestone. 
May Hill district—Longhope, &c., Upper Ludlow rock. 
Tortworth district—Pyrton Passage, Upper Ludlow rock. 
Usk district—Usk Castle, Upper Ludlow rock ; Llanbadoc, Aymestry limestone. 
Builth district—Henllyn, Pencarreg, Upper Ludlow rock. 
In his work on ‘British Palaeozoic Fossils’ Prof. M’Coy adds that D. rugata is 
common in the hard Upper Ludlow rock of Benson Knot, Kendal, Westmoreland ; in the 
same rock at the north end of Potter’s Fell, Kendal; at Burton and Brockton, near 
