Bracuiopopa. | LOWER PALAXOZOIC MOLLUSGA. 189 
centric laminar strize, about seventeen in the space of one millemetre ; several short slender conical spines are 
rather irregularly scattered over the surface, the substance of shell exhibiting under a high power an extremely 
minute reticular punctation. Average length (of rather large specimen) two lines, width usually rather less. 
This small species varies from nearly orbicular to ovato-pentagonal in outline ; in some specimens, par- 
ticularly those from Wellfield, the depressions left by the spines of the surface are very obvious and rather 
crowded, producing a puckered irregularity of the surface, which is not to be seen in most of the specimens from 
Pen Cerrig; the concentric lineation is also more distinct in the former, between which the reticular punctation 
is so excessively minute that it can only be traced with very fine and powerful glasses, in favourable lights, on 
the best preserved portions of the shell, differing therefore very much from the most nearly-allied fossil, the 
so-called Terebratula hamifera of Barrande. In nearly all the specimens, the distinct and rather large circular 
opening at the apex of the beak is easily seen, and in many specimens an irregular fissure, apparently produced 
by crushing, extends a variable distance towards the front margin, either in the medial line, or more or less to 
one side or the other. The few rather large concentric waves, or interruptions of growth, are only seen in some 
specimens. 
This species seems to agree in every thing with the little Terebratula hamifera (Bar.) (Haidingers 
Naturwissenschaftliche Abhandlungen, Vol. I. p. 418, t. 20. £. 9), but has the reticular punctation infinitely more 
minute than he describes that of his species to be (half a millimetre long, or four in a square millimetre). 
M. Barrande gives the geological place of his species in Bohemia as “ Gehdért der Quartzitetage (p) an, d. h. 
dem am hdéchsten gelegenen Theile des untern silurischen systems von Boéhmen,” and the schists in which it 
occurs in such profusion in Britain seem to hold precisely the same place. Its gregarious habits are curiously 
shewn by the circumstance of a fragment of shale four or five inches long and wide, from Pen Cerrig, having 
afforded upwards of a hundred specimens now in the collection ; and another mass, not much larger, from Well- 
field, having yielded upwards of seventy. 
Position and Locality—Very common in certain spots in the black shale of Pen Cerrig, Builth, Radnor- 
shire, and not uncommon in the olive schists of Wellfield, Builth, Radnorshire ; very rare in the olive schists of 
Pentre, Llangynyw, near Welchpool, Montgomeryshire. 
Explanation of Figures: —P\. 1. H. fig. 3. Several specimens, natural size, on portion of shale, from three 
miles North of Builth.—3 a perforated valve, magnified four diameters. 
Genus. ORBICULOIDEA (D’Ord.) 1847. 
Syn. = Schizotreta Kutorga, 1847—8. 
Gen. Char.—Both valves conical; shell corneous, not punctured; muscle of attachment pedunculated, 
passing through a hole near the beak of the smaller valve, in the distal end of a closed, fissure-like, longi- 
tudinal depression. 
Dr Kutorga’s deseriptions were probably read in 1847, but not published till 1848. (See the Proceedings 
of the Royal Mineralogical Society of St Petersburg for those years). 
ORBICULOIDEA IMPLICATA (Sow. Sp. ?) 
Ref. and Syn.? = Patella implicata Sow. Sil. Syst. t. 12. f. 14a. = Schizotreta elliptica Kutorga, Verhandl. 
der Russ. Kaiser. Min. Gesellschaft. zu St Petersburg. for 1846, t. 7. f. 7, and 1847, t. 7. f. 6. 
Sp. Ch.—Longitudinally oval, about one-fifth longer than wide, apex of the perforated valve at about 
two-fifths the length from the anterior edge, and the same length from the lateral edges; surface with 
slightly unequal and irregular sharp elevated concentric lines, about nine in the space of one line. Length 
about six lines, or rather more; width slightly less than five lines. 
In the Orbicula (Orbiculoidea) Forbesii (Davidson), both as figured in the Bulletin of the Geol. 
Society of France (Oct. 1848), and in the Memoirs of the British Geological Survey, the outline is a 
broader oval than in our specimens, and the distance from the beak to the anterior margin is less than from 
the same point to the lateral margin at right angles to the length; I do not therefore unite the species, 
