LAMELLIBRANCHIATA. | UPPER PALAOZOIC MOLLUSCA. 485 
on the anterior ear; body of the shell nearly smooth, marked with fine, close, concentric lines under the lens. 
Length about ten lines, proportional width from beak to opposite margin 7, length of posterior ear #, of 
anterior ear 4, depth of one valve 55. 
The radiating lines on the ears, and their absence on the concentrically lined, nearly smooth body of the 
shell, easily distinguish this species. I have some doubts of the true genus of this fossil, as the interior of one 
of the Derbyshire specimens shews a small cavity, which I cannot be certain is an accidental fracture, or the 
cartilage pit of Pecten. 
Position and Locality—Not uncommon in the black beds over the main carboniferous limestone of 
Derbyshire. 
AVICULOPECTEN CONOIDEUS (M*‘Coy). 
Ref. and Syn. = Pecten conoideus M*Coy, Syn. Carb. Foss, t. 17. f. 2. 
Dese.—Ovate, slightly oblique, subtriangular, left valve very gibbous, especially at one-third the length 
from the beak, which is narrow, but prominent; very strongly defined from the ears by an abrupt slope on 
each side; apical angle about 80°; posterior ear large, flattened, defined, slightly pointed, and with fine 
radiating close ridges ; body of the shell with numerous smooth, equal, rounded, radiating strize, about their own 
diameter apart, spaces between them flat, smooth, (about eight in the space of one line at half an inch from the 
beak). Width (of small specimen) from beak to opposite margin seven lines, proportional length ~, depth of 
left valve =. 
The Lowick specimen seems to differ from the one I originally described in the radiation of the ears, but 
this may have been obscured by the mode of preservation of the latter in an oolitic bed near the base of the 
carboniferous series. 
Position and Locality—Impure limestone of Lowick. The original Irish locality was, oolitic beds of 
lower limestone of Townplots, Killala. 
AVICULOPECTEN DOCENS (M‘*Coy). PI. 3. E. figs. 6 and 7. 
Ref. and Syn.= Pecten flexuosus M°Coy, Syn. Carb. Foss. t. 18. f. 1. (not Pecten flexuosus Lamk.) 
Desc.—Gently convex, right valve less so, broad-ovate, nearly orbicular; apical angle 105°, with from 
forty-five to sixty irregular, rounded, narrow, subequal (except at the sides near the beak where they alternate) 
radiating ribs, slightly roughened by small laminze of growth, and about their own thickness apart, with an 
occasional slight, irregular flexuosity; ears strongly defined, moderate, the posterior one falcate, pointed, 
sharply imbricated, parallel with the outer margin, crossed by three or four obscure, radiating, narrow ribs, 
a little longer than the anterior ear; anterior ear nearly square, or with a slightly oblique, sigmoid termination, 
flattened and yery abruptly defined by a narrow, vertical, smooth flexure from the body of the shell, with im- 
bricating strize parallel to the margin, crossed by two or three obscure narrow ridges near the hinge-line ; a deep 
rounded notch separates this ear from the body of the shell. Length one inch eleven lines, proportional width 
from beak to opposite margin *%, length of posterior ear #4, of anterior ear ;5,, greatest depth (about middle) of 
left valve |2,, width of cartilage facet nearly one line in middle, narrowing to a point at each end. 
_ All the ridges are continued to the beak, they are therefore very fine and close in the rostral part of the 
shell, there being about ten in three lines at an inch from the beak, and about four in the same space at the 
margin. The internal impressions are nearly smooth, with a broad fringe of short radiating ridges, like those of 
the exterior, round the margin, and frequently shewing the pallial line and large, single, muscular impression 
a little on the posterior side of the middle, likewise the narrow facet of the external cartilage along the hinge- 
line, and the absence of any cartilage pit under the beak, and thus as it were teaching me the generic dif- 
ference from Pecten, I haye, as above, changed my old specific name, which was preoccupied. 
