LAMELLIBRANCHIATA | UPPER PAL/EOZOIC MOLLUSCA. 483 
of a circle. Length of very large specimen three inches nine lines; in proportion thereto, width from beak to 
ventral margin ;*, length of hinge-line from beak to posterior angle *, depth of right valve 22. 
The smoothness of the surface will at once distinguish this species from its congeners ; the surface is 
slightly but uniformly convex ; the anterior ear is less than half the length of the posterior; the anterior side is 
dilated, so as to give a slight obliquity to the outline. Except the difference in size I do not see any difference 
between the English and Irish specimens, the latter being only an inch and half long. 
Position and Locality —Rare of large size in the impure carboniferous limestone of Lowick, Northumber- 
land. (The original localities were lower limestone of Millicent, Kildare ; Curkeen Rush and Howth, Dublin ; 
limestone, Ardagh). 
STREBLOPTERIA PULCHELLA (JM‘Coy). 
Ref. and Syn. = Meleagrina pulchella M°Coy, Syn. Carb. Foss, t. 12. f. 6. 
Desc.—Obliquely ovate, gently convex, greatest depth a little above the middle; anterior side long, 
straight, abruptly deflected, forming a narrow, highly inclined slope; posterior side and ventral margin semicir- 
cularly rounded; hinge short; ears obtuse; middle of the shell with about twenty radiating ridges in pairs, 
each pair separated from the rest by a broad shallow concavity, equalling the pair of ridges and intermediate 
furrow in width, the ridges rendered slightly nodular by minute, obsolete, concentric rugee ; a narrow portion of 
the anterior and posterior ends of the shell smooth. Length about six lines, proportional width from beak 
to ventral margin rather more, depth of right valve ;;, length of posterior wing 3. 
This pretty little shell may be known from the other mountain-limestone species by its large angular ribs, 
running in pairs from the beak to the margin; they are obscurely nodulose on the convex middle part of the 
body, where they are faintly crossed by minute, obtuse, concentric furrows, becoming obsolete at the sides. 
This is a scarce fossil; the specimen I have figured is more tubercular than the English one. 
Position and Locality—Rare in the lower limestone of Lowick, Northumberland. (The original locality 
was lower limestone, Millicent). 
Genus. AVICULOPECTEN. See page 392. 
AVICULOPECTEN C@LATUS (M‘Coy). PI. 3. E. fig. 5. 
Ref. and Syn. = Pecten cwlatus M*Coy, Synop. Carb. Foss, t. 18. f. 2. 
Dese.—Gently convex, most so at one-third from the beak, gradually flattening to the margins, rounded ; 
apical angle 110°; length and width almost equal; about sixty simple, subequal, narrow, rounded, radiating ribs, 
their own thickness apart, (at one inch from the beak in the middle of the shell there are five in two lines), 
each closely set with small, arched, imbricated scales, slightly more than the thickness of the ridge apart ; ears 
moderate, slightly pointed, with five or six narrow radiating ridges, nearly twice their thickness apart, crossed 
by rather closer, strong, curved ridges, parallel to the margin. Width one inch nine lines, length of ear nine 
lines, proportional depth of one valye 74. 
The very numerous, simple, nearly equal ribs, and the remarkably sharp, regular, vaulted scale-like sculp- 
turing, distinguish this rare species. 
Position and Locality—Rare in the impure carboniferous limestone of Lowick, Northumberland. The 
original Irish localities were, red limestone, Armagh ; lower limestone, Red Barn, Cookstown. 
Explanation of Figures.—P. 3. E, fig. 5, left valve, natural size; fig. 5 a, do. portion of surface magnified. 
AVICULOPECTEN CANCELLATULUS (M°Coy). PI. 3. E. fig. 3. 
Ref. and Syn, = Pecten cancellatulus M°Coy, Syn. Carb. Foss. t. 14. f. 9. 
Dese.—Ovate, gently convex towards the beak; apical angle 95°; ears large, deeply defined from the 
body of the shell; posterior ear large, falcately pointed, extending nearly as far as the edge of the shell, crossed 
