Bracuriopopa.| LOWER PALAZOZOIC MOLLUSCA. 251 
LINGULA ATTENUATA (So2.) 
Ref —Sow. Sil. Syst. t. 22. f. 13. 
Sp. Ch.—Obscurely subpentagonal, moderately and broadly convex from the beak along the middle nearly 
to the front, so that only a narrow margin all round is compressed, rather abruptly ; sides subparallel, very 
slightly compressed ; front obtusely subtruncate, gently convex ; posterior lateral margins long, nearly straight, 
forming an obtusely rounded angle with the sides, converging to the beak at a clearly defined angle of 70°; 
surface with minute lines of growth, and with traces of delicate longitudinal strize about the middle under the 
lens when decorticated. Length five lines, proportional width , depth about 33. 
This species is perhaps most allied to the Z. ovata (M°Coy), but is considerably shorter and wider, and has 
longer posterior lateral margins, besides being very much smaller. These differences becoming greater as the 
specimens of the two species approach each other in size. 
Position and Locality—tThin sandy Bala beds, E. of Nant y Groes, S. of Bala, N. Wales. 
LINGULA CORNEA (Sov.) 
Ref. = 1d. Sow. Sil. Syst. t. 3. f. 3. +L. minima Sow. Sil. Syst. t. 4. f. 49. and t. 5. f. 23. 
Sp. Ch.—Longitudinally oblong ; sides straight, parallel, rather abruptly inflected to form the posterior 
lateral margins, which are slightly convex, and join at the beak at an angle of 115°; anterior lateral angles 
abruptly rounded from the nearly straight sides to the nearly straight front; both valves broadly gibbous along 
the middle, so that only a narrow, nearly uniform space round the front and lateral margins slopes; greatest 
depth at rather more than one-third from the beak; surface marked with very numerous small, slightly and 
irregularly undulated, close wrinkles of growth, parallel with the margins ; substance of the shell thick, often 
whitish, very glossy when partially decorticated ; dull and yellowish brown when the periostraca is preserved, 
and then marked with very close, minute, slightly irregular, rugged, parallel strize (about twenty-four to twenty- 
eight in one line) ; no external radiating strize, but faint traces of extremely minute radiating lines on the middle 
of some internal casts; casts of one valve shew a very long, close pair of parallel sulci, one-fourth of a line 
apart (impressions of ridges on the shell) reaching nearly three-fourths the length to the anterior margin, the 
anterior extremity forming a rounded depression. Length of average specimens seven lines, proportional 
width =, depth = (some rare specimens nine lines long). 
This isan extremely constant and rather well-marked species, with an unusually thick shell, and remarkable 
for the nearly uniform gibbosity of the greater part of the valves; the proportional width is the only character 
which I have noticed to vary. The L. minima does not shew the slightest difference that I can perceive. 
Position and Locality.—V ery abundant and gregarious in the Upper Ludlow quartzite of Benson Knot, 
Kendal, Westmoreland ; not uncommon in the Upper Ludlow rock near Ludlow, Shropshire. 
LinevuLa curta (Conrad). 
Ref.—Hall, Pal. New York, t. 30. f. 6. and Conrad, Journ. Nat. Se. Phil. Vol. VIII. t. 15. f. 12. 
Sp. Ch.—Outline very regularly broad-ovate, greatest width slightly in front of the middle; front 
elliptically rounded, broad ; posterior lateral margins slightly arched, gradually converging to the small, sharp- 
pointed beak; valves flattened, slightly and evenly convex, becoming gradually compressed at the margins ; 
surface with minute, subregular, imbricating lines of growth; under the lens when decorticated very fine, faint, 
longitudinal strize, principally traceable about the middle. Length four lines, proportional width =, depth 32. 
The regular, broad-ovate form, narrow, pointed beak, and semielliptical front, easily distinguish this 
species from all others in the British rocks. The correspondence with the American Utica slate and Trenton 
lime species seems perfect in all respects. 
Position and Locality.—Rare in the calcareous Bala flags of Wellfield, Builth, 
KK2 
