LAMELLIBRANCHIATA., | LOWER PALHOZOIC MOLLUSCA. 261 
PTERINEA LINEATA (Gold.) 
Ref—ld. Gold. Pet. Germ. t. 119. f. 6. 
Sp. Ch.—Aliform, tumid; beaks rather large, obtuse ; posterior wing very large, gradually compressed, 
acutely pointed, extending beyond the respiratory margin, its posterior edge nearly straight above, much 
curved below; respiratory angle broadly rounded; ventral margin oblique, gently convex; posterior slope 
obscurely defined in old specimens; entire surface uniformly radiated with close, fine, unequal lines (about five 
in one line near the middle of the shell), less than their thickness apart, crossed by occasional, small, concentric 
waves of growth. Length from beak to respiratory angle one inch and half a line, from beak to end of hinge- 
line one inch; proportional width at right angles to middle of hinge-line ;5. 
The Avicula lineata, as figured by Sowerby (Sil. Syst. t. 5. f. 10), seems altogether different, by its 
greater obliquity, and its stronger, fewer, and more distant ridges—M. d’Orbigny proposes to call it A. lincatula 
(Prodrome, p. 33.) 
Position and Locality Rare in the Upper Ludlow micaceous quartzites of Benson Knot, Kendal, West- 
moreland ; in the fine sandy schists of Middleton Park, Caermarthenshire. 
: 
PTERINEA MEGALOBA (M‘Coy). PI. 1. I. fig. 19, 20. 
Ref—I\d. M*Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. p. 61. 
Sp. Oh.—Obliquely subtrigonal ; diagonally tumid from the beak to the posterior end (the curve amounting 
nearly to a semicircle in old specimens) ; hinge-line elevated into a compressed, nearly rectangular, broad wing, 
the angle rather nearer to the beak than to the posterior ventral end, which is obtusely rounded, and to which 
the margin is nearly straight ; anterior end short, forming a very large rounded lobe ; a shallow concavity, which 
defines it from the body of the shell, extends from the beak to a little in front of the middle of the ventral 
margin, where it forms a small sinus: beaks narrow, prominent, incurved; anterior muscular impression very 
strong in the casts; no teeth. Length from anterior to posterior ends one inch one line; proportional width 
from beak to opposite ventral margin ,j,; width of posterior end 4, depth of left valve 4. Surface apparently 
smooth, or marked with fine concentric striz. 
The great size of the anterior lobe is the most remarkable character, and is produced by the byssiferous 
sinus extending backwards at an acute angle to the hinge-line (about 75°), unlike any other species I know. 
Only for the left valve being so much more convex than the right, the species might have been placed in 
Cypricardites; the general form is exactly that of the Pterinea rectangularis (Sow. Sp.), Sil. Syst. t. 8. f. 2, 
from which it seems to differ (nine specimens examined) in the want of the diverging cardinal teeth. 
Position and Locality.—Not uncommon in the tilestone of Storm Hill, Llandeilo. 
Explanation of Figures.—P\. 1.1. fig. 19 and 20. Small specimens of left valve, natural size. 
PTERINEA PLEUROPTERA (Conrad Sp.) PI. 1.1. fig. 1. and 2. 
Ref. and Syn. = Avicula pleuroptera (Conrad) Journ. Acad. Se. Phil. Vol. VIII. t. 13. f. 2. 
Sp. Ch.—Body of the shell obliquely ovate, gently gibbous, most so towards the beaks, which are narrow 
and prominent above the hinge-line; anterior wing small, compressed, subtrigonal, strongly defined from the 
body of the shell; posterior wing about twice and half to three times the length of the anterior one, pointed, 
scarcely extending beyond the shell; its posterior margin concave, the posterior half of its dorsal edge 
thickened into a ridge, defined by an impressed line below; ventral margin obliquely rounded to the obtuse 
posterior end; surface (of left valve) with close concentric lines, sharpest on the wings, reticulated on about the 
middle portion of the shell by close, fine, subequal lines from the beak (about four in one line). Length 
from beak to posterior end ten lines (probably obliquely pressed) ; proportional length of hinge-line @ ; depth of 
both valves =; width at right angles to middle of hinge-line ;;. Larger and more quadrate specimen, from 
beak to posterior end one inch three lines, hinge from anterior to posterior wing the same, proportional width 
at right angles to middle of hinge '"* 
100° 
