Avicula. 
CONCHIFERA. 
163 
A. quadrata. Sowerby, Goo. Tr. 2d Ser. V. pi. 30, fig. 17. 
Sub-quadrangular, convex ; binge-line straight; anterior 
auricle small, rounded ; posterior auricle not defined ; a keel 
extending from the beak to the basal margin, which is 
rounded. 
^ The Coal Measures, Coalbrook Dale. 
40. Avicula discors. —Tho Discordant Avicula, pi. 
LXVI.** fig. 3. 
A. discors . Brown, Trans. Manch. Geo. Soc. I. p. 56, pi. 
VI. fig. 28. 
Smooth, oblique ; anterior side short acute, posterior side 
broad; superior auricle large; the inferior one small and 
parallel with the hinge-line; beaks small and prominent ; 
length a quarter of an inch; breadth nearly three-eighths. 
The New Red Sandstone, Newton, near Manchester. 
41. Avicula antiqua. — The Ancient Avicula, pi. LXI.** 
fig. 5. 
A. antiqua. Goldfuss, pi. 160, fig. 9. 
Obliquely sub-orbicular; hinge-line straight; auricles rather 
large; the anterior slightly defined ; the posterior one large; 
concave on the edge; whole surface with numerous, longitu¬ 
dinal, oblique, divergent strong ribs, with from one to three 
smaller intervening ones; crossed by many concentric, broad, 
shallow lines of growth. 
Upper Silurian Limestone, Westmoreland. 
42. Avicula lunulata. —The Crescent-shaped Avicula, pi. 
LXVII. fig. 17. 
Gervillia lunulata. Phillips, Geo. York, II. p. 211, pi. 
6, fig. 12. 
Very oblique, and much arcuated; hinge-line greatly ob¬ 
lique ; auricles unequal; tho anterior one short and blunt; the 
posterior very long, and acute at the upper angle; posterior 
side much lengthened, and with pretty strong concentric 
ridges; anterior side short; the beaks obtuse; surface with 
slight imbricated striae. 
The Carboniferous Limestone, Bolland. 
43. Avicula N eptune.— Neptune’s Avicula, pi. LXI.** f. 21. 
Sub-orbicular, sub-compressed ; hinge-line horizontal; auri¬ 
cles unequally undefined; anterior ono short; posterior 
projecting, in a line with tho side, and acute; whole surface 
with numerous, divergent, rounded, narrow ribs, with some¬ 
times smaller intervening ones ; crossed by very close, numer¬ 
ous concentric, raised etrke; anterior side rounded; posterior 
sido rather straight. 
The Upper Silurian Limestone, 'Westmoreland. 
44. Avicula tenera. —The Tender Avicula,pi.LXI.**f. 11. 
A, papyracea. Goldfuss, pi. CXVL fig. 5. 
Sub-orbicular, oblique; hinge-line nearly horizontal; auri¬ 
cles unequal; the anterior small and well defined ; the poste¬ 
rior large and undefined ; concave on the edge ; whole sur¬ 
face covered with numerous oblique, divergent, somewhat 
unequal ribs, most of them with a central groove, the ribs as 
well as tho intervening furrows crossed by numerous close-set, 
strong stria?; sides and base rounded. 
The Coal Measures, Bradford. 
45. Avicula pectinata. —The Pectinated Avicula, nl. 
LXVI.** fig. 2. 
A. pectinata, Sowerby, Geo. Trans. 2d. Ser. IV. p. 338. 
pi. 14, fig. 3. 
Obliquely-elongated, slightly arcuated, and a little convex ; 
hinge-line straight and horizontal; beaks obtuse and produced 
above tho hinge area ; auricles large ; the posterior one con¬ 
cave on the margin, as well as on the side of the valve ; ante¬ 
rior side convex and rounded, and surface with alternately 
long and short linear ridges. 
The Lower Greensand, ltisborougb, Kent. 
46. Avicula simplex. — The Simple-ribbed Avicula, pi. 
LXV. figs. 26, 27. 
Peclm simplex. Phillips, Geo. York, II. p. 212, pi. 6, fig. 
27. 
Obliquely-elongated ; hinge-line straight and oblique ; auri¬ 
cles nearly equal; lower valve tumid ; the surface with stron" 
divergent ribs and furrows; upper valve rather Hat, with 
tho furrows and ribs corresponding to the other, but shallower 
and flatter. 
The Carboniferous Limestone, Bolland. 
47. Avicula sub-rapiata. —Tho Sub-rayed Avicula, pi. 
LXI.** fig. 29. 
A. sub-radiata. Sowerby, Geo. Tr. 2d Ser. V. pi. 34, fig. 1. 
Phillips, Pal. Foss. pi. 23, fig. 86. 
Obliquely and transversely elongated ; breadth extending 
the whole length of the shell; hinge-line horizontal; one 
valve flat, tho other convex ; auricles not defined, the poste¬ 
rior ono smooth, with a few concentric lines, with radiations 
along the middle; anterior side narrow and pointed ; poste¬ 
rior side broad, and a little concave ; surface with remote ra¬ 
diating lines, crossed by raised concentric lines of growth. 
The Devonian Shales, Petherwin. 
48. Avicula cvonipes. —Tho Sw’an's-foot Avicula, pi. 
LXVI.** fig. 17. 
A. cygnipes . Phillips, Geo. York, I. p. 134, pi. 14, fig. 
3. Pecten cygnipes. Young and Bird, Geo. Sur. York, 
Coast, p. 235, pi. 9, figs. 4 and 6. 
Sub-quadrate, oblique ; lowx*r valve convex, the other fiat; 
hinge-line straight, oblique; umbo of the convex valve 
rounded and obtuse, projecting above the hinge area; auricles 
veryuneqnal, the anterior one exceedingly small and pointed ; 
the posterior one very large, concave on the edge, the point 
obtuse, and protruding beyond tho sido; surface with from 
four to five longitudinal, divergent, curved rib9, inclining pos¬ 
teriorly, and extending half an inch beyond tho margins, ter¬ 
minating in acute points; the intercostal spaces covered with 
fine longitudinal striae; lower margin concave between the 
ribs; flat valve with furrows corresponding in number to the 
ribs of the other valve, and with rather coarser, longitudinal 
stria* between the furrows, and with a f w concentric lines of 
growth towards tho base, the auricles ami hinge-line corre¬ 
sponding with the under valve. 
The Ironstone Bands in tho Aluminous Strata, near Whitby, 
and in the Lias at Bilsdale and Wilton Castle, Yorkshire. 
49. Avicula longicostata. —The Long-Ribbed Avicula, 
pi. LXVI.** figs. 15, 16. 
A. longicostata . Stutchbury, Mag. Nat. Hist. 1839, p. 163, 
fig. 28. 
Ovate, inequivalve, the lower one convex and the upper 
fiat; lower valve with the hinge-line horizontal, and a little 
curved; ears very unequal, the anterior one extremely small 
and obtuse, the posterior very large, somewhat rounded 
