80 BRITISH SILURIAN BRACHIOPODA. 
common in the schists of the Caradoc or Bala limestone at several places near Bala, 
Merionethshire ; also at Pont-y-Glyn Diffwys, West of Corwen, in the same county ; and 
it occurs in the Llandeilo grits of Tan-y-Craig, Builth ; also at Bala Lake. 
Mr. Prosser sent me an internal cast (the one I figure) of the ventral valve which 
he had found in the shales of the Bala limestone near Llanfyllin. It occurs also in Den- 
bighshire, south-east of Cerrig-y-Druidion. In Ireland it is exceedingly abundant, always 
in the condition of internal casts and impressions, in the Caradoc slates of the Chair of 
Kildare,’ Cahiranearla. It is also found at Grangegeeth, Kildare; and at Frankfort and 
Newtown Head, Waterford. From these localities fine series of specimens have been 
obtained for the Museums of the Geological Survey in London and Dublin. 
Crania ImpLicata, Sow. sp. Pl. VIII, figs. 13—18. 
PATELLA IMPLICcAaTA, Sow. Silurian System, pl. xii, fig. 14 a, 1839. 
ORBICULOIDEA ImpLicaTa, M‘Coy. British Pal. Foss., p. 189, 1852. 
Cranta? impiicata, Salter. Siluria, 2nd ed., pl. xx, fig. 4, 1899. 
Spec. Char.—Shell very small, longitudinally oval, free, or unattached; slightly 
inequivalve ; ventral valve gently convex, highest part or vertex sub-central, being closer 
to the posterior than to the anterior edge, and marked with concentric, slightly raised, 
or step-like bands of growth. Dorsal valve rather deeper than the opposite one, limpet- 
like, the pomted apex being likewise nearer to the posterior than to the anterior 
margin ; surface marked with concentric lines of growth, less prominent than those on 
the other valve. The interior of the ventral valve shows a broad, flat, concentrically 
striated margin, with two small, narrow, oval-shaped divaricator muscular scars, obliquely 
placed, and in close contiguity to the posterior portion of the flattened margin, but sepa- 
rated from each other in the middle by a space about equalling half the length of 
one of the impressions; towards the middle of the concave valve two ovate, slightly 
depressed occlusor or adductor muscular impressions are visible, and separated from each 
other by a small, tongue-shaped, slightly raised, flattened projection, these impressions 
bemg hkewise somewhat elevated in front. The interior of the dorsal valve is at present 
unknown. 
Length about 2, width 23 lines. 
Obs. This little shell appears to have puzzled more than one paleontologist. In 1839 
Sowerby described it as follows : 
“ Patella ? implicata, fig. 14a. Oval, depressed, surface composed of concentric lamine; 
1 An interesting account of the Lower Silurian rocks of the Chair of Kildare, by Mr. G. V. Du 
Noyer, will be found in the description accompanying Quarter-sheet 35 N.E. of the Map of the Geological 
Survey of Ireland, 1858. 
* «Discina” in the Appendix, p. 542. 
