236 BRITISH PALASOZOIC FOSSILS. [Bracuroropa, 
valve, nearly vertical, inclining backwards only at 115°; receiving valve subpyramidal, greatest depth near 
the point of the beak, which is only slightly incurved; a very obscure trace of mesial furrow; surface radiated 
with coarse angular ridges, dichotomising once or rarely twice between the beak and margin, separated by 
narrower sulci, which are strongly punctate; ten or twelve ridges in the space of one line near the margin : 
entering valve nearly flat, interior with a small prominent rostral tooth; a strong mesial septum, reaching 
nearly to the front margin, and two rather long cardinal teeth, diverging at 150°; the inner surface marked 
with four or five irregular rows of extremely large punctures or small pits. Average width two lines, pro- 
portional length 5, depth about ;;;. 
Position and Locality—Extremely common with the ZL. dwvigata in the thin flaggy beds of Wenlock 
shale at Gwyddelwern, Derwen, near Corwen, Denbighshire; olive Wenlock shale of Llanfair, Welchpool ; 
ealeareous flags, bed of Dee, Llantsilio, S. of Llangollen ; in decomposing bands of limestone above Rother 
Bridge. 
LEPTHNA OURALENSIS (M/. V. K.) 
Ref.—Murchison, de Verneuil, and Keyserling, Geol. Rus. t. 14. f. 1. 
Sp. Ch.—Subhemispherical, slightly depressed ; front margin semicircular ; hinge-line exceeding the width 
of the shell, forming obtusely rounded convoluted ears, separated by a shallow concavity from the body of the 
shell, which is evenly gibbous, strongly and regularly arched from the beak to the front margin, the greatest 
depth being at about the middle of the length ; entering valve nearly as concave as the receiving one is convex ; 
cardinal area low, triangular, nine or ten times wider than high: surface marked with strong filiform, radiating 
striz, between each pair of which are from five to nine much smaller, close, slightly undulating, parallel strize, 
the sulei between which are strongly punctured, the whole being crossed with extremely minute transverse 
lines of growth ; about thirty-five strize in two lines at four lines from the beak, four of which are large (twenty- 
five in the same space at margin, three of which are large) ; interior surface closely and strongly pitted with minute 
punctures, and rather broad, (four or five in two lines from the margin,) slightly undulating, longitudinal, obsolete 
ridges, more or less branched towards the margin. Width two and half inches, proportional length ;;, depth 
2 distance between the valves one line. 
This very remarkable species has exactly the form and size of the Producta hemispheerica of the mountain- 
limestone, and the same extremely narrow space for the animal between the valves, so that it might easily be con- 
founded with it by a careless observer ; the striation, however, as pointed out by the authors of the Geology 
of Russia, easily distinguishes the species, even when the distinct cardinal area is invisible; the substance 
of the shell is also very much thinner. Our specimens agree in every respect with those of the Oural, 
which are said to characterize the Upper Silurian rocks there. 
Position and Locality—Not uncommon in the limestone between Old Radnor and Presteign, Rad- 
norshire. 
LEPTHNA QUINQUECOSTATA (A/*Coy). Pl. 1. H. fig. 30, 31, 32. 
Ref. and Syn. = Orthis quinquecostata (M°Coy), Sil. Foss. Irel. t. 3. f. 8. 
Sp. Ch.—Nearly semicircular; hinge-line exceeding the width of the shell, forming acutely angular, convex 
ears; middle of receiving valve very gibbous ; profile much curved from the inflection of the obtuse beak to the level 
of the lateral margins; cardinal area narrow, placed in the plane of the lateral margins ; entering valve concave, 
about one-third the depth of the receiving valve, each valve with usually five, very large, prominent, angular ridges, 
about a line apart, radiating from the beak, each with a strong radiating line along its keel, intervening 
spaces between each pair concave, marked with ten or fifteen fine, sharp, longitudinal striz (sixteen in the 
space of one line in middle of front margin); close to the beak, and extending only one-third the length of the 
shell, are two short similar ridges, one on each side of the mesial one; in some specimens an additional pair of the 
large radiating ridges are developed at the sides, not reaching, however, to the beak : internal cast of receiving 
