426 
MOLLUSCA. COKBULADtE. Mactiia. 
EXTINCT SPECIES. 
1. C. Gibbose, when young suborbicular, when old transversely 
oblong ; anterior side produced, recurved ; surface concentrically furrowed 
near the beaks ; posterior side beset with short spines. Sower. Min. Conch, 
t. ccix. f. 5, 6, 7* — Green Sand. 
2. C. IcBvigata. — Orbicular, gibbose, smooth, and thin ; beaks prominent, 
incurved. Sower. Min. Conch, ccix. f 1, 2. — ^een Sand. 
3. C. glohosa. — Globose, smooth ; anterior side of the large valve produced 
into a lip ; truncated ; beaks equal. Sower. Min. Conch, t. ccix. f. 3 — Lon- 
don Clay. 
4. C. Pisiim. — Subglobose, irregular, concentrically furrowed ; anterior side 
slightly truncated ; margin of one valve produced ; beaks equal — Sower. Min. 
Conch, t. ccix. f. 4. — London Clay. 
5. C. revoluta. — Transversely oblong, tumid, transversely furrowed ; ante- 
rior side produced, truncated, with a carina running to the beak ; margin of 
the larger valve prominent, inflected ; beaks equal. Sower. Min. Conch, t. 
ccix. f. 8, 13 — London Clay. 
C. C. nitida — Ovate, subtrigonal, equilateral, gibbose, anteriorly truncated, 
smooth, valves nearly equal. Sower. Min. Conch, t. ccclxii. f. 1, 2, 3. — Upper 
Marine Formation^ Isle of Wight. 
7 . C. cuspidata. — Transversely oblong, tumid, unequivalved, subequilate- 
ral ; anteriorly carinated and cuspidated ; lower margin of the left valve ex- 
panded and inflated. Sower. Min. Conch, t. ccclxii. — Upper Marine Forma- 
tion^ Isle of Wight. 
8. C. complanata. — Transversely oval ; elongated, depressed, and sulcated ; 
sulci few ; anterior side smallest, subtruncated and defined by an obtuse 
ridge ; left valve enclosing the other. Sower. Min. Conch, t. 362. f. 7? 8.— • 
In Crag. 
9. C. limosa — Transversely subtriangular, and longitudinally heart-shaped ; 
beaks gibbous, surface slightly striated by the layers of growth ; the shell 
thin. I have this shell from slate-clay, connected with carboniferous limestone ; 
the shell usually adheres greatly to the substance of the bed. 
MACTRAD.^. 
Gen. CXII. MACTRA. — Shell subtriangular, a little gaping ; 
beaks protuberant ; hinge with one spoon-shaped tooth in 
each valve, and an adjacent heart-shaped cavity ; in one 
valve there is a single lateral plate on each side closing be- 
tween two in the other. 
^ Lateral teeth striated ; the shell strong. 
444. M. solida.—Shell subtriangular, subdepressed from the 
beaks at both extremities, with the line of junction slightly pro- 
minent ; nearly equilateral. 
