AUAMELLIBRANCHIATA. | LOWER PAL/EOZOIC MOLLUSCA. 263 
rock, Benson Knot, Kendal, Westmoreland; High Thorns, Underbarrow, Kendal, Westmoreland: (erect. 
var. y.) tilestone of Horeb Chapel, Llandovery, S. Wales; Upper Ludlow, Laverock Lane: (var. 8. naviformis) 
Wenlock limestone, Dudley, Staffordshire ; very common in the Upper Ludlow rock, Kirkby Moor, Kendal, 
Westmoreland. 
PTERINEA SOWERBIL (J/*Coy). 
Ref. and Syn. = Avicula reticulata (Sow.) Sil. Syst. t. 6. f. 3 (not of Hisinger nor Goldfuss). 
Sp. Ch.—Obliquely ovate, depressed, slightly convex, greatest length along the posterior slope, which is 
straight and defined; posterior wing gently arched, scarcely extending beyond the shell; its posterior edge 
slightly and uniformly concave; surface radiated by slightly irregular obtuse ridges, about their thickness apart 
(five in two lines about the middle, at one inch from the beak), partially interrupted by thin concentric im- 
brications from one to two lines wide, having the radiating ridges obsolete, or nearly so, on their rostral half ; 
radiating ridges of the wing rather larger, strongly marked only about the middle. Length from beak to 
44 
respiratory angle two inches six lines; length of posterior wing *, width of ditto =; width from middle of 
hinge-line to ventral margin =, depth of one valve =. 
This fine species differs from the Pterinea reticulata of the original continental authors. in its more elongate 
form, smaller posterior wing, with its gently concave posterior edge, and the comparatively few, broad, thin 
imbrications interrupting the radiating ridges. 
Position and Locality.—Aymestry limestone, Leintwardine, Shropshire. 
PTERINEA SUBFALCATA (Conrad Sp.) Pl. 1.1. fig. 3. 
Syn. and Ref.= Avicula subfalcata (Conrad) Journ. Acad, Philad. Vol. VIII. t. 13. f. 4. 
Sp. Ch.—Body of the shell obliquely ovate, subfalcate, narrow, convex ; beaks gibbous, prominent ; anterior 
wing defined by a sinus, narrow, compressed, rounded, about half the length of the posterior wing, which is flat, 
abruptly defined from the body of the shell, and is acutely pointed with a concaye posterior margin ; entire surface 
radiated with subequal, thread-like ridges, about their thickness apart and about ten in the space of one line of 
the margin (more distant on the posterior wing), crossed by rather more distant concentric ridges, most distinct 
on the wings, and about equalling the radiating ones in thickness. Length from beak to posterior end four 
lines, of posterior wing =, width of ditto ,, width from beak to opposite ventral margin ~. 
The narrow subfaleate figure of the body of the shell renders this little species easily recognisable. 
Mr Conrad only figures the unradiated or right valve, though he describes the radiations of the other, which 
I figure. 
Position and Locality—V ery common (small variety) in the shale of Howgill Fell, near Sedburgh, Kendal, 
Westmoreland ; the larger variety (nine lines from beak to posterior end) occurs in the grey micaceous flagey 
quartzite at Benson Knot, Kendal, Westmoreland, and in a similar matrix near Pont-ar-y-llechan, Llandeilo. 
Explanation of Figures.—P1. 1. I. fig. 3. Natural size, left valve, from Howgill Fell; fig. 3 a, ditto, mag- 
nified. 
PTERINEA TENUISTRIATA (J/°Coy). PI. 1.1. fig. 4. 
Ref.—ld. Ann. Nat. Hist. 2nd Series, Vol. VII. p. 62. 
Sp. Ch.—Subquadrate, rounded, slightly oblique, evenly gibbous, left valve most so; length only slightly 
exceeding the width; beaks large, tumid; anterior wing half the length of posterior one, abruptly compressed, 
rounded; ventral margin and posterior end broadly rounded; posterior margin slightly concave towards the 
cardinal angle of the posterior wing, which is gradually compressed, and scarcely extends beyond the shell ; 
surface with irregular concentric wrinkles of growth crossed by very fine, equal or subalternate radiating strize 
from the beak, strongest in the middle, about six in one line, less than their diameter apart; posterior lateral 
