Bracuropopa. | LOWER PALAZOZOIC MOLLUSCA. 187 
Ist Family. CRANIADZ (@0O7?.) 
Shell thick, pyramidal, calcareous, without muscle of attachment; free or fixed by the substance of 
the lower valve; arms spirally fixed among themselves, not extensile, nor supported by apophyses ; 
thickened margin of the valves with ramified impressions of the fimbriated edge of the mantle. 
The family contain two genera:—Ist, Crania; 2nd, Pseudocrania. 
Genus. PSEUDOCRANIA (AfCoy). 
Ref.— M°Coy, Ann. Nat. Hist. 2nd Series, Vol. VIII. p. 387. 
Gen. Char.—Shell slightly inequivalve, free; both valves regular, depressed, subconical, unattached ; 
dorsal valve with or without a small cardinal area; internally, margin broad, flat, smooth, or minutely 
striated concentrically ; anterior pair of muscular impressions much larger and more strongly marked than 
the posterior pair; pallial impressions numerous, linear, not interrupted along the middle. 
This Paleozoic genus differs from the true Craniw in the following points: Ist, Crania is attached 
by the substance of the dorsal valve, and exhibits thereon an irregular scar,—both valves are free and 
regular in Pseudocrania; 2nd, in Crania the posterior or marginal pair of adductor muscles are always 
larger and deeper than the medial or anterior pair; the reverse is remarkably the case in the present 
genus, which also has a smooth or minutely striated margin, destitute of the strong granulation and 
punctures of most Craniw. The Crania antiquissima, as given by Verneuil, may be taken as the type of 
the genus, as also the following species. 
PSEUDOCRANIA DivanicaTa (M°Coy). Pl. 1. H. figs. 1 and 2. 
Ref—MCoy, Ann. Nat. Hist. 2nd Series, Vol. VIII. p. 388. 
Sp. Ch.—Longitudinally oblong, length and width almost equal, slightly narrowed posteriorly; hinge- 
line straight, a little shorter than the width of the shell; dorsal valve (analogue of the lower or attached 
valve) with a very low triangular cardinal area; external surface ornamented with sharp, prominent, narrow, 
rugged lines divaricating from the beaks, those of the sides arched backwards towards the cardinal angles, 
about equally distant throughout, from the intercalation of shorter striz, as the longer approach the margin ; 
intervening spaces flat, about four ridges in the space of one line: internal casts shew a broad, flat, 
defined rim, with minute irregular concentric strive, and the following parts in relief (depressions in the 
shell): Ist, a small oval mesial space originating near the hinge, and reaching to one-fourth of the length ; 
2nd, on each side of this, close to the hinge-margin, are two diverging oval muscular impressions; 8rd at 
a little behind the middle of the shell are two ovate, subtrigonal, anterior, muscular impressions; considerably 
larger and deeper than the posterior pair; 4th, close in front of these, a narrow semicircular impression 
(visceral aponeurosis?), with its extremities arching backwards round the muscular impressions; 5th, 
between this and the front and lateral margins a series of from fifteen to twenty-two uninterrupted, equi- 
distant, longitudinal, narrow, pitted, pallial impressions, each dividing at its anterior half, separated by rather 
wider, smoother spaces. Length ten lines, greatest width (a little in front of the middle) ten and one- 
third lines, height of cardinal area three-fourths of a line. 
In size and general character this agrees with the Pseudocrania antiquissima (Kichw. Sp.), as given 
by M. de Verneuil (Geol. Russia, t. 1. fig. 12), but is easily distinguished externally by the beak being 
close to the posterior margin, and by the remarkably divaricating sculpture of the valves, and internally 
by several minor points of detail, obvious on comparing the figures. 
Position and Locality—Common in the schists on the Bala limestone at Bryn-Melyn quarry near Bala, 
Merionethshire; schists of Pont y Glyn, Diffwys, West of Corwen, Merionethshire; and in the fine grits 
of Tan y Craig, Builth. 
Explanation of Figures.—P\. 1. H. fig. 1. From the Upper Bala rocks of Bryn Melyn, Bala. Natural 
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