168 



COXCHIFERA. 



Pern- 



Genus XXX.— POSIDONIA.— ^roKK. 



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-depressed ; interior with one muscu- 

 lar impression. 



1. PosiDONiA coMPLANATA. — The Compressed Posidonia, 

 pi. LXI.»» fig. 33. 



P. complanata. Portlock, Geo. Rep. p. 472, 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 transversa. — The Transverse Posidonia, pi. 

 LXI.** fig. 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, Ferraanah, 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 mindta. — The 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 Poudoiiux minuta of Bronn and Goldfuss. Their 

 shell is obliquely orbicular, pi. LXI.** fig. 40. 

 The Keuper Sandstone, Bunge Hill Quarries. 



5. Posidonia lateralis. — The Lateral Posidonia, pi. 

 LXI.*»» fig. 2. 



P. lateralis. Sowerby, Geo. Tr. 2d Ser. V. pi. 52, fig. 1. 

 Phillips, Pal. Foss. p. 45, pi. 20, fig. 74. 



Transversely elongated, oblong-ovate, oblique, and com- 

 pressed ; beaks situate near the anterior extremity ; surface 

 with concentric angular ridges. ■ 



The Carboniferous Limestone, Venn,- Barnstaple, Swim- 

 bridge, and Brampton, North Devon, and Lew Trenchard, 

 South Devon. 



e. Posidonia Becheri. — Becher's Posidonia, pi. LXI.** 

 fig. 35. 



P. Becheri. Sowerby, Geo. Tr. 2d Ser. V. pi. 52, fig. 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, Venn, Swimbridge, &c., and 

 the Devonian Shales, Herborn. 



7. Posidonia anodontoidea. — The Anodon-shaped Posido- 

 nia, pi. LXI.*"* fig. 1. 



P. Becheri. Sowerby, Geo. Tr. 2d Ser. V. 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 strise, which is a characteristic of 

 most of the shells of this genus. 



This species might easily be mistaken for an Anodon. 



The Carboniferous Limestone, Venn. 



8. Posidonia truncata. — The Truncated Posidonia, pi. 

 LXI.** fig. 26. 



P. Becheri. Var. Sowerby, Geo. Tr. V. 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-set concentric ridges, with very narrow fur- 

 rows ; and also with very minute concentric strire. 



I agree with Mr Sowerby that this surely cannot be the P. Becheri. 



The Carboniferous Limestone. 



9. Posidonia tuberculata. — The Tuberculated Posidonia, 

 pi. LXI.** fig. 34. 



P. tuberculata. Sowerby, Geo. Tr. 2d Ser. V. 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 the ribs. 



Carboniferous Limestone, Budle, Northumberland, and Venn, 

 Swimbridge. 



10. Posidonia vetusta. — The Ancient Posidonia, pi. 

 LXVII. fig. 15. 



Inoceramm veiustus. Sowerby, VI. p, 162, pi. 584, fig. 2. 



Sub-ovate, rather convex ; beaks prominent ; both slopes 

 considerably oblique; sides a little straight, and rounded below ; 

 surface smooth, with broad concentric ribs, and shallow fur- 

 rows ; anterior side with a concave space resembling a lunette. 



The Carboniferous Limestone, Castleton and Settle, York- 

 shire. 



Genus XXXI.— PERNA.— 5r?«^Mwm 



Shell sub-equivalve, flattened, and somewhat irregular, a 

 little distorted, thickish, and externally lamellar ; the laminte 

 composed of minute perpendicular fibres ; beaks small, nearly 

 equal, and situate at the posterior extremity of the hinge 

 margin ; hinge linear, marginal, with numerous transverse, 

 parallel, opposite grooves, which, together with flattened ridges 

 between them, are destined for the reception of the ligament ; 

 the anterior extremity of the 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 the 

 byssus ; with a parietal callosity, which is more distinct in the 



