426 MOLLUSCA. CORBULADiE. Mactua. 



EXTINCT SPECIES. 



1. C. yiganlea — 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. laevigata — Orbicular, gibbose, smooth, and thin ; beaks prominent, 

 incurved. Soiver. Min. Conch, ccix. f. 1, 2. — Green Sand. 



3. C. globosa. — 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. Pisum — Subglobose, irregular, concentrically furrowed ; anterior side 



slightly truncated ; margin of one valve produced ; beaks equal Soiver. Min. 



Conch, t. ccix. f. 4. — London Clay. 



5. C. rcvoluta — 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. Soiver. Min. Conch. I. 

 ccix. f. 8, 13. — London Clay. 



0. C. nitida — Ovate, sub trigonal, 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^E. 



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. 



