Sphenia. MOLLUSCA. MYAD.E. 465 
581. L. Mans. — Retral extremity slightly produced, with 
the dorsal margin nearly straight and subrecurved. 
Mactra hians, Pult. Dorset, 32 — Don. Brit. Shells, t. cxl. Mmt. Test. 
Brit. 101 L. oblonga, Turt. Biv. Brit. 64. t. v. f. 6. — In sand, be- 
yond low- water mark. 
Length 2\ inches, breadth 5 inches ; thick, coarsely striated ; it chiefly 
differs from the last in its shortness, great breadth, the straightness of the 
dorsal and ventral margins, and the subrecurved aspect of the posterior ex- 
tremity. In the L. vulgaris the syphon-mark has a smooth polished border ; 
in this species the margin is a little raised. 
The following shells, which Dr Turton has included in his genus Monta- 
cuta^ with the following character : “ Shell oval or oblong, equivalve, inequi- 
lateral ; mostly closed ; hinge with two teeth in each valve, and a cavity be- 
tween them ; lateral teeth none ; ligament internal,” appear to be the fry of 
the species of the genera Mya and Lutraria, before they have begun to bur- 
row in the sand or mud. 
1. substriata — Shell oval, with obscure longitudinal ribs ; |th of an inch in 
length ; Ligula substriata^ Mont. Test. Brit. Sup. 25. — M. substriata, Turt. 
Biv. Brit. 59 — Adhering to Corallines and the spines of Echini. 
2. Udentata. — Shell oval, smooth, with one of the teeth oblique and spoon- 
shaped — Mya Udentata, Mont. Test. Brit. 44. t. xxvi. f. 5.— M. bid. Turt. Biv. 
Brit. 60. — In cavities in old Oyster Shells. 
ferruginosa. — Shell oblong, slightly striated transversely, with one of the 
teeth incurved and spoon-shaped. — Mya fer. Mont. Test. Brit. Sup. 22. t. xxvi. 
f. 2 — M. fer. Turt. Biv. Brit. 60 — In Sand and Clay. 
4. oblonga — Shell oblong, smooth, with all the teeth erect. — M. ob. Turt. 
Biv. Brit. 61. t. xi. £ 11, 12 In Sand. 
EXTINCT SPECIES. 
1 . L. gibbosa — Tletral side widest, recurved, truncated and gaping.— 
Min. Conch, t. xlii. — Oolite. 
2. L ? striata. — Transversely oval, compressed, concentrically striated ; pos- 
terior side smallest, rather pointed, gaping ; beaks prominent. — Sower. Min. 
Conch, t. Dxxxiv. f. 1. — Green Sand. 
3. L ? carinifera. — Transversely oval, elongated, convex, longitudinally 
striated ; posterior side smooth, bounded by an obtuse carina, truncated, its 
edge straight. — Sower. Min. Conch, t. Dxxiv — Lower Chalk. 
4. L ? oblata. — Compressed, transversely oval, with obtuse extremities 
slightly bent ; beaks prominent. — Sower. Min. Conch, t. Dxxxiv. f. 3. — Lon~ 
don Clay. 
Gen. CXLI. SPHENIA. — Transverse, inequivalve, inequi- 
lateral, open retrally ; hinge of the right valve with an 
elevated transversely dilated tooth, of the left valve with a 
concave tooth, and small denticle before it. — Turton. 
582. S. Binghami. — Shell wedge-shaped, with the concave 
tooth oblique and inflected. 
Turt. Biv. Brit. 36. t. cxi. f. 4, 5. and t. xix. f. 3. — In rocks, Torbay. 
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