168 
CONCH I FEU A. 
Pehn a. 
Genus XXX.— POSIDONIA.— Broun . 
Shell free, roundish oval, inequilateral, both sides with 
rudimentary, rounded, not well defined auricles; cardinal area 
linear, thick, and toothless, with a fusiform, striated canal 
below the beaks, anteriorly extended ; beaks equal, sub-medial, 
generally obtuse, and sub-depressod ; interior with one muscu¬ 
lar impression. 
1. Posidonia complanata. —The Compressed Posidonia, 
pi. LXI.** fig. 33. 
P. complanata. Portlock, Geo. Rep. p. 4*72, pi. 34, 
fig. 12. 
Inequivalve, transverse, oblong-ovate, one valve a little 
convex, the other quite flat, and enveloped by the opposite 
one; hinge-line nearly straight; beaks nearly obsolete; surface 
with fine concentric lines of growth ; breadth not an eighth of 
an inch. 
The Carboniferous Limestone, Ballynascreen, Derry, Ire¬ 
land. 
2. Posidonia trans versa. —The Transverse Posidonia, pi. 
LXI ** lig. 25. 
P. transversa. Portlock, Geo. Rep. p. 745, pi. 38, fig. 9. 
Transverse, slightly oblique, and compressed ; beaks obtuse 
and rounded, placed near the anterior margin; surface with 
strong, transverse folds. 
The Carboniferous Limestone, Fermanah, Ireland. 
3. Posidonia venusta. —The Handsome Posidonia, pi. 
LXI.** fig. 38. 
P. venusta. Portlock, Geo. Rep. p. 424, pi. 25 A, fig. 4. 
Transversely oval, frequently oblique, generally concentri¬ 
cally wrinkled, and striate ; the ear large, separated from the 
rest of the shell by a slight bend ; umbo short, projecting a 
little beyond the hinge-line. 
Silurian Limestone, Tyrone, Ireland. 
4. Posidonia minuta. —Tho Small Posidonia, pi. LXI.** 
fig. 32. 
P. minuta. Sowerby, Geo. Trans. 2d Ser. Y. pi. 28, fig. 4. 
Sub-triangular, rather inflated ; umbo large, obtuse ; surface 
with transverse wrinkles. 
This is not Posidonia minuta of Broun and Goldfuss. Their 
shell is obliquely orbicular, pi. LXI.** fig. 40. 
The Kouper Sandstone, Bunge Hill Quarries. 
5. Posidonia lateralis. —Tho Lateral Posidonia, pi. 
LXI.*** fig. 2. 
P. lateralis. . Scwerby, Geo. Tr. 2d Ser. Y. pi. 52, fig. l t 
Phillips, Pal. Foss. p. 45, pi. 20, fig. 74. 
Transversely elongated, oblong-ovate, oblique, and com¬ 
pressed ; beaks situate near tho anterior extremity; surface 
with concentric angular ridges. 
Tho Carboniferous Limestone, Yenn, Barnstaple, Swim- 
bridge, and Brampton, North Devon, and Lew Trenchard, 
South Devon. 
G. Posidonia Becheri. —Bochers Posidonia, pi. LXI.** 
fig. 35. 
P. Beclieri. Sowerby, Geo. Tr. 2d Ser. Y. pi. 52, tig. 3. 
Phillips, Pall. Foss. p. 45, pi. 20, fig. 73. 
Obliquely sub-triangular, compressed, with numerous con¬ 
centric ridges, and very fine concentric stria?, which are 
hardly visible without the aid of a lens; posterior slope 
straight; umbones nearest the anterior side. 
The Carboniferous Limestone, Yenn, Swimbridge, &c., and 
the Devonian Shales, Ilerborn. 
7. Posidonia anodontoidea. —Tho Anodon-slmpcd Posido- 
nia, pi. LXI.*** fig. L 
P. Becheri. Sowerby, Geo. Tr. 2d Ser. Y. pi. 52, fig. 2. 
Transversely oblong-ovate; posterior slope lengthened, 
oblique, and narrowed at the termination; hinge-line curved; 
umbones obtuse ; anterior side short and obtuse ; whole sur¬ 
face covered with numerous, rather close, very narrow, concen¬ 
tric ridges, separated by a narrow groove ; towards the mar¬ 
gins the ridges become mere stria), which is a characteristic of 
most of the shells of this genus. 
This species might easily he mistaken for an Anodon. 
The Carboniferous Limestone, Yenn. 
8. Posidonia trdncata. —The Truncated Posidonia, pi. 
LXI.** fig. 2G. 
P. Becheri. Yar. Sowerby, Geo. Tr. Y. 2d Ser. pi. 52, 4. 
Sub-quadrate, a little oblique; hinge-line nearly straight 
and horizontal; anterior side very short, and considerably nar¬ 
rower than the posterior, which is large, sloping obliquely from 
the hinge-line, and obtuse below; umbones obtuse; surface 
with many close-sot concentric ridges, with very narrow fur¬ 
rows ; and also with very minute concentric stria?. 
I agree with Mr Sowerby that tliis surely cannot be the P. Becheri. 
The Carboniferous Limestone. 
9. Posidonia tuberculata. —Tho Tuborculated Posidonia, 
pi. LXI.** fig. 34. 
P. tuberculata. Sowerby, Geo. Tr. 2d Ser. Y. pi. 52, fig. 5. 
Phillips, Pall. Foss. p. 44, pi. 25 A, fig. 4. 
Sub-triangular, compressed, somewhat elongated; umbones 
nearly central; surface with many concentric ridges, and three 
or four longitudinal slight ribs, which produce a tuberculated 
appearance, as they cross tho ribs. 
Carboniferous Limestone, Budle, Northumberland, and Yenn. 
Swimbridge. 
10. Posidonia vetusta. —The Ancient Posidonia, pi. 
LXYII. fig. 15. 
Inoceramus vetustus. Sowerby, YI. p. 162, pi. 584, fig. 2. 
Sub-ovate, rather convex; boaks prominent; both slopes 
considerably oblique; sides a little straight, and rounded below; 
surface smooth, with broad concentric ribs, and shallow fur¬ 
rows ; antoriorsido with a concave space resembling a lunette. 
The Carboniferous Limestone, Castleton and Settle, York¬ 
shire. 
Genus XXXI.—PER NA.— Bruguiere. 
Shell sub-equivalve, flattened, and somewhat irregular, a 
little distorted, thickish, and externally lamellar ; the laminae 
composed of minute perpendicular fibres ; beaks small, nearly 
equal, and situate at the posterior extremity of the hinge 
margin; bingo linear, marginal, with numerous trausverse, 
parallel, opposite grooves, which, together with flattened ridges 
between them, are destined for the reception of the ligament; 
the anterior extremity of tho hinge is narrower than its poste¬ 
rior termination ; situate immediately under the extremity of 
the hinge margin is a posterior sinus, for the passage of tho 
byssus; with a parietal callosity, which is more distinct in the 
