190 BRITISH PALAOZOIC FOSSILS. | Bracniopopa. 
but provisionally refer it to the so-called Patella implicata (Sow.), with the proportions of which it agrees 
very well. If the reference to Sowerby be rejected the species should bear Dr Kutorga’s specific name. 
Position and Locality.—In the olive Ludlow-beds above the second grits, Keeper’s Lodge, Goldengrove, 
Llandeilo, Cacrmarthenshire ; a crushed example possibly of this species in the fine Ludlow Rock above 
Parklane, Llandeilo. 
Genus. DISCINA (Lam.) 
= Orbicula (Auct. not of Cuvier). 
Gen. Char.—Shell corneous, not punctured, muscle of attachment not pedunculated, passing through 
a slit in the flat dorsal valve, the opposite valve obliquely conical. 
Prof. Fleming and Mr J. E. Gray have satisfactorily shewn that the shells commonly called Orbicula, 
properly belong to the genus Discina of Lamark—Orbicula of Cuvier being a synonym of Crania. 
Discina Morrist (Davidson Sp.) 
Ref. and Syn. = Orbicula id. id. Bull. de la Soe. Géol. de France. 2nd Series, Vol. V. t. 3. f. 47. 
Sp. Ch.—Nearly orbicular, length slightly exceeding the width; imperforate valve gently convex, surface 
remarkably even and smooth; beak obtuse, at about one-third the length from the posterior end, with a 
short, narrow, internal longitudinal ridge, extending a short way from it towards the anterior margin; 
entering-valve slightly concave at the margins and at the anterior half, tumid towards the opening, which 
is very broad oval, half its length from the posterior margin, the intervening space being about one-sixth 
the entire length. Length about seven lines, proportional width about ;;;, depth ;5,. 
This species is easily distinguished from the Discina rugata by its nearly smooth surface, having its 
beak rather farther from the margin, and wider fissure, and from the Orbiculoidea implicata by its less 
elongate form, and wanting the sharp concentric ridging. 
Position and Locality—Not uncommon in the Lower Ludlow rock of Leintwardine, Shropshire. 
DiscInA RUGATA (Sow. Sp.) 
Ref. = Orbicula id. Sow. Sil. Syst. t. 5. f. 11. 
Sp. Ch.—Rotundato-subtrigonal, or nearly orbicular, usually a little wider than long, but sometimes the 
length slightly greater than the width, depressed; apea about one-fifth the length from the margin, height 
varying from one-third, to rather less than one-fifth the length; surface very glossy, marked with sharp 
interrupted, irregular, concentric wrinkles, (sometimes, in soft rocks more regular) separated by comparatively 
wide spaces, six or seven in the space of one line, crossed in some specimens by faint coarse radiating 
strie ; interior of attached valve flat, slightly tumid towards the apex, which is nearly central, and from 
which a broad oval perforation extends rather more than halfway to the margin; the concentric lines 
rather more regular than in the large valve. Average length four lines. 
The substance of this species is distinctly corneous when preserved in sandstone (though apparently 
caleareous in limestone) and unpunctured, and I cannot see why M. d°Orbigny places it in his shelly pune- 
tured genus Orbicella. I have not seen any specimens quite so coarsely wrinkled as Mr Sowerby’s. In one 
group the specimens within a few inches of each other varied from having the length and width equal, to 
having the width one-fifth greater than the length. Few of the specimens shew the radiating strie in parts. 
Position and Locality.x—Common in the hard Upper Ludlow rock of Benson Knot, Kendal, West- 
moreland; in same rock, north end of Potter’s Fell, Kendal, Westmoreland; Upper Ludlow rock of Wool- 
hope; Upper Ludlow rock of Burton and Brockton; Upper Ludlow rock near Ludlow, Shropshire. 
