Bracuiopopa. | LOWER PALAOZOIC MOLLUSCA. 245 
extremities, partially defining the very small muscular impressions, which reach little more than one-third the 
length of the shell, (rarely two-fifths) : entering valve gently convex, with a linear, nearly obsolete cardinal area ; 
a strong bifid rostral tooth, forming two small pits in the cast ; two short, very divergent cardinal teeth, recurved 
so as nearly to touch the cardinal line with their distal ends, and having between them a very short obtuse 
mesial ridge, (leaving a short broad obtuse furrow in the cast), only extending about one-sixth the length of the 
shell: striation of both valves coarse, strong, varying greatly in prominence of particular lines, (apparently from 
the state of preservation,) seeming in some specimens obscurely alternate, while in others, or parts of the same 
specimen, every 8rd, 5th, or 7th line, much more prominent than the rest; all rugged with minute, close, 
transverse strize, the sulci marked each with a row of very small punctures; from twelve to sixteen of the 
radiating lines at six lines from the beak in the space of two lines. Width one inch nine lines, proportional 
length usually /", or 5; (occasionally only ,;;,) depth (greatest at a little in front of middle of entering valve) |<. 
100 
This is distinguished from the O. expansa by the much coarser strize, the smaller muscular impressions, 
and the slight concavity of the receiving valve, as well as the characters of the cardinal area. Some of the 
varieties, if ill preserved, are scarcely distinguishable from certain states of S. compressa. 
Position and Locality —Common in the flaggy limestone of Ravenstone Dale, Westmoreland; fine Caradoc 
sandstone of Horderly; Bala sandstone of Bodean, Pwllheli, Caernarvonshire; Bala schists of Cefn Coch, Glyn 
Ceiriog, Denbighshire; ? Bala schists of Blaen y ewm, W. of Nantyre, Glyn Ceiriog, S. of Llangollen, 
Denbighshire ; ¢ Bala limestone of Meifod; Bala schists of Cyrn y Brain, Wrexham, Denbighshire; ? Bala 
schists of Cefn Coedog, Corwen, N. Wales; not uncommon in the Bala schists of Gelli Grin, Bala, Merioneth- 
shire ; rare in the fine sandstone of May Hill, Gloucestershire ; common of small size in the Bala quartzite of 
Llanwddyn, E. of the Berwyn Mountains. 
LerTta@NA (Strophomena) PECTEN (Linn. Sp.) 
Ref. and Syn.= Anomia pecten Linn. Syst. Nat. =Orthis pecten Dal. Act. Holm. 1827. t. 1. f. 6. 
(not of Sow. Sil. Syst.) Davidson, Geol. Journ. t. 13. f. 8 to 23. 
Sp. Ch.—Transversely semielliptical or obscurely subtrigonal; greatest width along the hinge-line, very 
much depressed ; receiving valve slightly concave towards the margins, slightly prominent at the beak, which 
is elevated by the cardinal area, which is flat, triangular, about eight times wider than high, inclining backwards 
at an angle of 130°; triangular foramen half closed by a pseudo-deltidium, flanked on the cast by two very short, 
straight, dental lamellze, diverging at 100°, between which there are no visible muscular impressions; receiving 
valve slightly convex along the middle, most so near the beak, flattened towards the sides; cardinal area 
flattened, triangular, about twelve times longer than high, the foramen being closed by a large bifid rostral tooth: 
internal cast of entering valve with two deep, approximate, ovate pits (of the bifid rostral tooth) at the beak, from 
which on each side two very short, nearly straight dental lamelle, diverge at 120°, between which, and a very 
shallow, wide furrow, of a short mesial obscure ridge, may be observed the slight prominence of the obtusely- 
angular muscular impressions; both valves radiated with about sixty strong, nearly equal, straight, sharply- 
defined, thread-like ridges (about six in two lines) at the margin, separated by flat spaces, rather wider than the 
ridges, in which a very slender mesial ridge may be detected, flanked (under a strong lens) by one or two 
irregular, minutely-punctured striz. Width one inch four lines, proportional length *, depth about 7. 
This species is easily distinguished by its numerous, strong, straight, subequal ridges, between which 
there is rarely more than the single, fine, duplicating line to be distinguished ; the additional striae mentioned 
being very rarely visible, while the rest are sharply and distinctly marked. The species is also remarkable for 
the near equality in size of the cardinal area in the two valves; the internal strive generally mark the cast 
nearly to the beak; the puncturing is very minute. 
Position and Locality—Common in the Coniston (Bala) limestone of Coniston, Lancashire ; Bala schists 
¢ Blain y ewm, W. of Nantyre, Glyn Ceiriog, S. of Llangollen, Denbighshire ; limestone of Ravenstone Dale, 
Westmoreland; Coniston (or Bala) limestone of Applethwaite Common, Westmoreland; sandstone of Mid- 
dleton Park, Caermarthenshire ; Upper Bala rock of Capel Cerrig; sandstone of May Hill, Gloucestershire ; 
Horton in Ribblesdale, Yorkshire ; Woolhope limestone of Littlehope. 
