170 
CONCHIFERA. 
Mytilus. 
Conical, wedge-shaped; umbones obtuse; surface smooth, 
with a few transverse shallow wrinkles. 
The Cave Oolite, Clougkton, Yorkshire. 
7. Pinna aucuata.—T he Arcuated Pinna, pi 70, fig. 1. 
P. arcuata. Sowerby, IV. p. 10, pi. 3J3, 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 strife or narrow furrows, separating the narrow 
llattened ribs ; opposite side smooth, with some nearly equi¬ 
distant, transverse lines of growth. 
The London Clay, High gate. 
8. Pinna folium. —The Leaf Pinna, pi. LXX. fig. 2. 
P. folium. Phillips, Geo. York, I. pi. 14*, 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 Boulbv 
Cliffs. 
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 surfaco, with a suture in 
the middle; section generally square. 
The Lower Greensand, Lympno and Pulborough, and the 
Greensand, Blackdowu 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, Clicl- 
ten ham. 
11. Pinna affinis.—T he 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, llighgato and Bognor. 
12. Pinna granulata.— The Granulated Pinna, pi. LXX. 
fig. 5. 
P. granulata. Sowerby, IV. p. 65, 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 Kirameridge Clay, Weymouth and Pabba. 
13. Pinna Hartmanni. —Hartmann'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 lozengo. 
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 XXXIII.—DREISSINA.— Van Beneden. 
Shell boat-shaped, or mytiliform ; valves carimated; 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 closiug muscle; anterior mar¬ 
ginal seam with a fissure near its centre, for the passage of the 
byssus. 
1. Dreissina Brardii. —Brard’s Dreissina, pi. LXXI. 
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 
arc somewhat arcuated. 
Lower Fresh-water Formation, Ilordwell. 
Genus XXXIV.—M YTILUS. — Linnaeus. 
Shell equivalve, regular, longitudinal, somewhat wedge- 
shaped, with the beaks terminating in a pointed summit; 
posterior sido rounded and closed ; base forming a continuous 
line with the interior margin, in a direction oblique to the 
hinge-line ; anterior margin gaping slightly in the centre for 
the passage of the byssus ; hinge destitute of teeth ; ligament 
marginal, linear, greatly elongated, and sub-internal; outside 
coverod with a strong horny epidermis; two muscular im¬ 
pressions, the posterior one largo and irregular, tlio 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 Wight. 
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 ; 
gibboso; beaks obtuse, nearly meeting when the valves are 
closed ; hinge with three or four slight teetli; surface smooth. 
The Maminiforous Crag, Bramorton. 
3. Mytilus edulis. —The Edible Mytilus, pi. LXXI. 
fig. 11. 
M. alaeformis. Sowerby, II. p. 133, pi. 275, fig. 4. 
Obovato; beak acuminated, curved, smooth ; hinge with 
three teeth ; side doeply indented, and forms a regular curve. 
The Mammiforous Crag, Norwich, and the Red Cra^, 
Bawdsey. 
4. Mytilus edentulus.— 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 
