484 BRITISH PALAZOZOIC FOSSILS. [LAMELLIBRANCHIATA. 
by thick close strize, parallel with its concave margin and terminating in little club-shaped scales on the hinge- 
line; anterior ear only half the length of the posterior, rounded, marked with thick, close ridges parallel with 
the end; body of the shell radiated with about twenty thick obtuse ridges, obscurely alternate in size, crossed 
by equally thick, concentric ridges, irregular, but about the same distance apart as the others, the points of inter- 
section forming little tumid bullze, or large tubercles occasionally rising into spines. Length four and half lines, 
width from beak slightly more than four lines, length of posterior ear two lines, proportional depth of one 
valve 3. 
I imagine the greater size of the English specimens and a small portion apparently broken off the side of 
the Irish one, will satisfactorily account for the difference in apical angle and number of ridges between the 
present more perfect example and that I originally figured. The species is strongly distinguished from all 
others by the very large spherical or conoidal nodules at the intersection of the concentric and radiating 
ridges. 
Position and Locality —Rare in the carboniferous limestone of Lowick, Northumberland. (My original 
locality was Killymeal, Dungannon). 
Explanation of Figures.—P1. 3. E. fig. 3, left valve magnified three diameters; fig. 3, outline of do. 
natural size. 
AVICULOPECTEN concavus (M‘Coy). Pl. 3. E. fig. 2. 
Ref. and Syn. = Pecten concavus M°Coy, Syn. Carb. Foss. t. 15. f. 10. 
Dese—Quadrato-orbicular, flattened; apical angle, including the undefined posterior ear, 150°; right 
valve gently convex, depressed ; left valve flattened, slightly convex near the beak, very slightly concave out- 
wardly towards the margin; covered by about one hundred and fifty to two hundred rough, radiating, thread- 
like ridges, less than their diameter apart, alternately larger and smaller on the body and posterior wing, about 
twenty-nine on the anterior ear; anterior ear nearly as long as the margin of the shell, nearly square, the edge 
slightly sigmoid; posterior ear undefined, extending slightly beyond the margin of the shell, the end slightly 
pointed by an obtuse re-entering angle in the posterior margin at one-third of its length below the tip. Length 
from anterior to posterior margin three inches nine lines, proportional width from beak to opposite margin 80°, 
length of anterior ear 4, depth of do. 4, length of posterior ear ;;,, depth of left valve 3, of right valve 
about 74; seven or eight ridges in the space of two lines at an inch from the beak. 
This large species has the left valve concave outwardly in most specimens (though only in a very slight 
degree towards the margin), in which it differs from all the other Paleozoic species. The opposite valve is 
slightly more convex, the whole appearing of a rather irregular growth (approaching Hinnites), and of a thin 
substance. 
Position and Locality—Not uncommon in the impure limestone of Brigsteer, and in the similar beds at 
Lowick, Northumberland. The original Irish locality was, very rare in the arenaceous limestone at Killala, 
Kallogunra. 
Explanation of Figures.—P1. 3 E. fig. 2, left valve natural size; fig. 2a, do. portion of surface magnified. 
AVICULOPECTEN CONCENTRICO-STRIATUS (M/°Coy). 
Ref. and Syn. =Pecten id. M*Coy, Synop. Carb. Foss. Irel. t. 14. f. 5. 
Desc.—Ovato-orbicular, slightly and evenly convex; apical angle varying from 105° to 110°; ears large, 
flattened, nearly equal, both strongly and abruptly defined from the body of the shell; anterior ear separated 
from the body of the shell by a deep acute notch, obliquely rounded at the extremity, reaching nearly as far as 
the margin of the shell, marked with six or seven strong, radiating ridges, crossed by slightly scaly lines of 
growth ; posterior ear faleate, acutely pointed, extending slightly beyond the posterior margin, from which it is 
separated by a rounded sinus, its surface radiated with twelve or more close, subequal strize, smaller than those 
