Orbicula. 



CONCHIFERA. 



143 



4. Orbicula graxttlata. — Tho Granulated Orbicula, pi. 

 XLIX. fig. 16 and 26. 



0. granulata. Sowerby, VI. p. 6, pi. 506, fig. 3, 4. 

 Brown's Elements Fossil. Conch, p. 75, pi. 9, fig. 10. 



Nearly orbicular ; conical, patcllieforni, with a rather 

 acute apex, and sides a little rounded ; surface with numer- 

 ous granulated radiating stria;, crossed by many lines of growth. 



Great Oolite, Ancliff, Wiltshire. 



5. Ordicula Humphriesiana. — Huraphrie's Orbicula, pi. 

 XLIX. fig. 8, 9. 



0. Hunipkr'umana. Sowerby, VI. p. 5, pi. 506, fig. 2. 

 Conical, orbicular ; conical, depressed; apex eccentric, and 

 rather obtuse ; surface with many divergent stria;. 

 Kimmeridge Clay, Shotover Hill, Oxfordshire. 



6. Orbicula reflexa. — The Reflexed Orbicula, pi. XLIX. 

 fig. 17, 18, 19. 



0. reflexa. Sowerby, II. p. 4, pi. 506, fig. 1. lb. Zool. 

 Jour. II. 321. 



Somewhat elliptical ; thin, surface smooth, polished ; 

 upper valve convex, covering the reflex edge of the lower 

 valve ; apex eccentric, placed very near to one end, lower 

 valve flat, with the vertex nearly central, and a reflexed 

 margin in consequence of the disc behind tho apex being con- 

 cave ; byssal sinus large and elongated. 



7. Orbicula latissima. — The very Broad Orbicula, pi. 

 XLVIII. fig. 35. Patella latissima, p. 105. 



Patella latissima. Sowerby, II. p. 88, pi. 139, fig. 1 and 5. 



Depressed, smooth, slightly ovate, and very thin ; vertex 

 eccentric ; surface concentrically undulated. 



Oxford Clay, Scarborough and Elberston. 



S. Orbicula nitida. The Shining Orbicula, pi. XLIX. 

 fig. 10, 21, and 22. 



0. nitiila. Phillips, Geo. York. II. p. 221, pi. 1], fig. 

 10, 11, 12, 13. 



Slightly ovate ; upper valve conico-lenticular ; apex obtuse, 

 situate near tho narrow end; surface covered with fine wide- 

 set stria;, radiating from the apex to the sides. 



Carboniferous Limestone, at Bowes, Pateley Bridge, Lee, 

 Ilarelaw, and Otterburn, Coalbrookdale. 



9. Orbicula mutabala. — The Changeable Orbicul.a, pi. 

 XLIX.* fig. 1. 



0. nitida. Portlock, Geo. Rep. p. 446, pi. 32, fig. U, 

 variety. 



Slightly ovate, glabrous, with somewhat irregular and 

 faintly defined lines of growth, and extremely fine radiating 

 strice, which can only be seen by the aid of a lens ; beak 

 remote, distant about one-fourth of tho diameter from the 

 margin, its elevation being about one-third of its diameter ; in 

 most instances, however, only about a fourth. 



Distingaisbed from 0. nitida hy the nearly obsolete very faint radiat- 

 ini; stria;. 



Carboniferous Strata, in Shale, at Benburb, Ireland. 



10. Orbicula cincta.— The Girdled Orbicula, pi. XLIX.* 

 fig. 9. 



0. cincta. Portlock, Geo. Rep. p. 446, pi. 32, fig. 15. 



Nearly circular, with fine concentric lines of growth ; 

 apex not a third of the diameter from tho margin, and ele- 

 vated about a third ; lower valve also convex, with a tmncated 

 apex. 



Carboniferous Limestone Shale, Benburb and Tyrone, Ire- 

 land. 



11. Orbicula laevigata. — ^The Smooth Orbicula, jil. 

 XLIX. fig. 10. 



0. livvii^ata. (Miinster.) — Portlock, Geo. Rep. p. 445, pi. 

 32, fig. 11, 12. 



Circular, highest towards the beak, which is only slightly 

 arched, short, and at the outer margin depressed ; shell smooth, 

 the lines of growth hardly visible. 



Silurian, gritty coarse Schists, Tyrone, Ireland. 



12. Orbicula oblongata. — The Oblong Orbicula, pi. 

 XLIX.* fig. 12. 



0. elotiffata. Portlock, Geo. Rep. p. 445, pi. 32, fig. 13. 

 Elongated, greatly flattened, and smooth ; beak slightly 

 raised, and situate near the margin. 

 Differs from 0. Ixvijala in the beak not being so close to the margin. 

 Silurian, gritty Schists, Tyrone, Ireland. 



13. Orbicula radiata. — The Rayed Orbicula, pi. LXIX.* 

 fig. 13. 



0. radiata. Phillips, Geo. York. I. p. 101, pi. 4, fig. 12. 



Slightly ovate ; apex placed near the narrow end ; general 

 surface smooth ; with a series of radiating stria; round the 

 margin. 



Coral Crag, Malton, Yorkshire. 



14. Orbicula subrotunda. — The Half-round Orbicula, 

 pi. XLIX.* fig. 14. 



0. subrotunda. Portlock, Geo. Rep. p. 445, pi. 32, fig. 10. 

 Slightly oval; apex situate one-fourth the diameter from 

 the margin. 

 Silurian Schists, Tyrone, Ireland. 



15. Orbicula Norvegica. — The Norwegian Orbicula, 

 pi. XLIX.* fig. 11. 



0. Norvegica. Lamarck, An. San. Vert. VI. pt. I. p. 242. 

 Brown's Illustrations of Recent Conchology of Brit. p. 6, pi. 

 20, fig. 21, 22, and pi. 22, fig. 9. 



Form irregular ; margin ruggid, upper valve pattelliform, 

 a little convex, with concentric lines of growth ; vertex a 

 little ofl" tho centre ; under valve quite flat, adhering its whole 

 circumference to other bodies ; provided with four muscular 

 impressions. 



Coral Crag, Sutton. 



Tribe II.— RUDISTA. 



Animal unknown, as are also the ligament and hinge ; shel 

 with very unequal valves, and destitute of distinct umbones. 



Genus XIV. HIPPONYX.— Dc/rance. 



Generic Character. — Shell bivalve, adherent, iuequivalve, 

 irregular; muscular impressions in both valves horse-shoe 

 shaped ; lower valve attixed to marine bodies, orbicular, much 

 compressed, and con.sidcrably thickened in some instances, 

 with its margins always elevated, particularly in front, its 

 muscular impression consisting of two contiguous semilunar 

 portions, which are distant, broad, and rounded in front, 

 nearly confluent and narrow behind; upper valve patelliforiu, 

 generally subconic, in some instances comjjressed, with a 

 posteriorly subniarginal umbo pointing backwards ; muscular 

 impressions situate near the posterior margin, with its two 

 lobes considerably more remote, and obliquely truncated in 



