Sphenia. mollusc a. MYADtE. 465 



58 L L. Mans. -^'Retra\ extremity slightly produced, with 

 the dorsal margin nearly straight and subrecurved. 



Mactra hians, Pull. 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 oJiiefly 

 differs from the last in its shortness, great breadtli, 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 mai'gin 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 Mi/a and Lutraria, before they have begun to bur- 

 row in the sand or mud. 



1. substriata — Shell oval, witli obscure longitudinal ribs ; ith 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. bidentata — Shell oval, smooth, with one of the teeth oblique and spoon- 

 shaped — Mya bidentata, Mont. Test. Brit. 44. t. xxvi. f. 5. — M. bid. Turt. Biv. 

 Brit. 60 — In cavities in old Oyster Shells. 



2. ferruginosa. — Shell oblong, slightly striated transversely, with one of the 

 teeth incurved and spoon-shaped — Myafer. 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. f 11, 12 — In Sand. 



EXTINCT SVECIES. 



1 . L. gibbosa — Hetral side widest, recurved, truncated and gaping Sower. 



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. £ 1. — Green Sand. 



3. L ? carinifera. — Transversely oval, elongated, convex, longitudinally 

 striated ; posterior side smooth, bounded by an obtuse carina, truncated, its 

 edge straight. — Sotver. 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. — Twton. 



582. S. Bhighami. — 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. 

 VOL. I. G g 



