170 



CONCHIFERA. 



Ml 



Conical, wedge-shaped ; umbones obtuse ; surface smooth, 

 with a few transverse shallow wrinkles. 

 The Cave Oolite, Cloughtou, Yorkshire. 



7. Pinna aecuata. — The Arcuated Pinna, pi. 70, fig. 1. 

 P. arcuata. Sowerby, IV. p. 10, pi. -313, fig. 3. 



Short, somewhat equilateral ; arcuated and ventricose ; 

 beaks obtuse, and considerably curved ; hinge-line gently bent : 

 depth and length nearly equal; anterior half with wide, shallow, 

 longitudinal striae or narrow furrows, separating the narrow 

 flattened ribs ; opposite side smooth, with some nearly equi- 

 distant, transverse lines of growth. 



The London Clay, Highgate. 



8. Pinna folium. — The Leaf Pinna, pi. LXX. fig. 2. 

 P. folium. Phillips, Goo. York, L pi. U, fig. 17. 

 Elongated, slightly curved ; sub-quadrate ; one side with 



oblique, transverse folds, the other with curved shallow folds ; 

 valves separated by a longitudinal ridge. 



The Lower Lias Shale, Robin Hood's Bay, and Boulby 

 Clifi"s. 



9. Pinna tetragona. — The Tetragonal Pinna, pi. LXX. 

 fig. 3. 



P. tetragona. Sowerby, IV. p. 9, pi. 313, fig. 1. 



Abruptly conical, narrow above and wide beneath ; a little 

 arcuated ; smooth, with obscure, longitudinal, slightly elevated 

 ribs, occupying more than half of the surface, with a suture in 

 the middle ; section generally square. 



The Lower Greonsand, Lympne and Pulborough, and the 

 Greensand, Blackdown and Isle of Wight. 



10. Pinna mitis. — The Buried Pinna, pi. LXX. fig. 4-. 

 P. mitis. Phillips, Geo. York, I. pi. 5, fig. 7. 

 Elongated, nearly straight ; beaks acute ; surface with con- 

 centric ridges. 



The Oxford Clay, Scarborough, and Inferior Oolite, Chel- 

 tenham. 



11. Pinna affinis. — The Allied Pinna, pi. LXX. fig. 6. 

 P. affinis. Sowerby, IV. p. 10, pi. 313, fig. 2. 



Nearly equilateral, ventricose, straight, wedge-shaped, 

 smooth, with irregular, longitudinal, divergent ribs, which, 

 however, only occupy the anterior portion of the valves, and 

 disappear near the edge. 



The London Clay, Highgate and Bognor. 



12. Pinna grandlata. — The Granulated Pinna, pi. LXX. 

 fig. 5. 



P.granulata. Sowerby, IV. p. 6.5, pi. 347. 



Broad, conical, nearly equilateral, convex ; anterior side 

 rounded, with a rounded elevation near the posterior side ; edge 

 very thick towards the anterior side ; surface obscurely decus- 

 sated ; length about eight inches, breadth six inches. 



The Kimmeridge Clay, Weymouth and Pabba. 



13. Pinna Hartmanni. — Ilartmann's Pinna. 

 P. Hartmanni. Goldfuss, pi. 127, fig. 3. 

 Longitudinal, conical ; surface with numerous, divergent, 



narrow, obtuse ribs, with close-set transverse striae ; a sharp 

 ridge rises from the beaks, and is lost about half-way down the 

 valve ; section of the shell lozenge. 

 The Oolite, Magilligan, Ireland. 



14. Pinna sulcata. — The Furrowed Pinna. 



P. sulcata. Woodward, Geo. Nor. pi. 5, fig. 23. 

 Considerably elongated, club-shaped ; anterior side with 



longitudinal, narrow furrows ; posterior side large, expanding 

 longitudinally ; furrowed and ribbed. 

 The Upper Chalk, Harford Bridge, Norfolk. 



Genus XXXIIL— DEEISSINA.— Fa« Beneden. 



Shell boat-shaped, or mytiliform ; valves carinatcd ; liga- 

 ment internal, except in a little fissure in both valves ; exter- 

 nally, a rude cardinal tooth is situate under the umbo in the 

 right valve, which locks into a corresponding cavity in the left 

 valve ; in the umbonal angles of both valves are placed trans- 

 verse partitions, for sustaining a closing muscle ; anterior mar- 

 ginal seam with a fissure near its centre, for the passage of the 

 byssus. 



1. Dreissina Brardii. — Brard's Dreissina, pi. LXX I. 

 figs. 3, 4. 



M. Brardii. Sowerby, VI. p. 60, pi. 532, fig. 2. 



Convex, straight, fusiform, elongated ; beaks acute, within 

 each of which there is a transverse plate for the tendon ; 

 beneath is a flat angular process towards the beak ; the valves 

 are somewhat arcuated. 



Lower Fresh-water Formation, Ilordwell. 



Genus XXXI v.— MYTILUS.—ZuwcBMs. 



Shell equivalve, regular, longitudinal, somewhat wedge- 

 shaped, with the beaks terminating in a pointed summit ; 

 posterior side rounded and closed ; base forming a continuous 

 line with the interior margin, in a direction oblique to the 

 hinge-line ; anterior margin gaping slightly iu the centre for 

 the passage of the byssus ; hinge destitute of teeth ; ligament 

 marginal, linear, greatly elongated, and sub-internal ; outside 

 covered with a strong horny epidermis ; two muscular im- 

 pressions, the posterior one large and irregular, the anterior 

 very small and terminal ; muscular impressions of the mantle 

 irregular ; destitute of a sinus. 



1. Mytilus affinis. — The Allied Mytilus, pi. LXXI. f. 16. 



M. affinis. Sowerby, VI. p. 59, pi. 532, fig. 1. 



Obliquely elongated ; sides parallel, straight; anterior mar- 

 gin reflected ; arcuated ; surface smooth, destitute of teeth. 

 Posterior side arcuated in the young shell. 



The Upper Marl, Colwell Bay, Isle of AVight. 



2. Mytilus antiquorum. — The Ancient Mytilus, pi. 

 LXXI. fig. 17. 



M. antiquorum. Sowerby, III. p. 133, pi. 275, figs. 1, 2, 3. 



Oblong-ovate ; length somewhat more than twice its width ; 

 gibbose ; beaks obtuse, nearly meeting when the valves are 

 closed ; hinge with three or four slight teeth ; surface smooth. 



The Mammiferous Crag, Bramerton. 



3. Mytilus edulis. — The Edible Mytilus, pi. LXXI. 

 fig. 11. 



M.alceformis. Sowerby, II. p. 133, pi. 275, fig. 4. 



Obovate ; beak acuminated, curved, smooth ; hinge with 

 three teeth ; side deeply indented, and forms a regular curve. 



The Mammiferous Crag, Norwich, and the Red Crag, 

 Bawdsey. 



4. My^tilus ebentulus. — The Toothless Mytilus. pi. 

 LXXI. fig. 1. 



M. edentulus. Sowerby, V. p. 55, pi. 439, fig. 1. 

 Elongated ; beak sharp, below which the shell is deep ; 

 disk obtusely carinated ; posterior side nearly straight ; front 



