376 MOLLUSCA. SESSILIA. Discina 



gin not waved ; hinge patulous, short. — Anomise striata, Urc, Ruth. 31 1. 

 t. xiv. £ 13, 14 — A. resupinatus, Marl. Derb. t. xlix. f. 13, 14 In Carboni- 

 ferous Limestone. 



16. S. Martini. — Transversely oval, convex, decussatedly striated ; the 

 longitudinal strife close, equal, minute ; the transverse ones broad, promi- 

 nent, remote ; beak incurved, pointed ; hinge patulous, short. — Anomitis 

 lineatis, Mart. Derb. t. xxxvi. f. 3. — In Carboniferous Limestone. 



17- S. Urii — Smooth, a mesial furrow in each valve, ending in front in a 

 straight wave of the margin; imperforate valve nearly flat, with a straight 

 gibbosity at the apex ; perforated valve with a gibbous lengthened incurved 

 beak; hinge patulous, short — Ure, "Ruth. 313. t. xiv. £ 12. — Carboniferous 

 Limestone. 



18. S. exaralus — Perforated valve with broad, smooth, flattened ribs, di- 

 vided by shallow narrow furrows ; beak gibbous, incurved, hinge very short. 

 I have frequently found the perforated valve of this well marked species, 

 but always mutilated, and without the other valve. — In Carboniferous Lime- 

 stone, West Lothian. 



Gen. MAGAS. — " An unequilateral unequivalved bivalve ; 



one valve with an angular sinus along an incurved beak ; 



line of the hinge and back of the other valve straight, with 



two projections near the middle. A partial longitudinal 



septum, with appendages attached to the hinge within. ri — 



( Soroerby.) 



1. M. pumilus. — The beaked valve is hemispherical, smooth, with a circu- 

 lar edge, and small, incurved beak ; the other valve nearly flat, with a long 

 transverse straight beak. — Sou-er. Min. Conch, t. cxix — In Chalk. 



SESSILIA. 



Gen. XCII. DISCINA.— Shell convex, upper valve with an 

 entire subcentral apex, under valve with the apex promi- 

 nent and pierced by an oblong fissure, for the passage of 

 the ligament. 



369- D. ostrcoides. — Upper valve with fine longitudinal ribs, 

 crossed by concentric wrinkles. 



Lamark, Hist. pt. i. 23C. — Orbicula Norvegica, G. B. Sowerby, Lin. 

 Trans, xiii. 468. t. xxvi. f. 2.— Habitat uncertain. 

 Length about ffcths, breadth T 4 5 ths of an inch ; brown, the lower valve 

 white ; the margin is more or less waved ; the ribs, as they proceed from the 

 apex, are slightly bent, the concentric wrinkles of growth are numerous and 

 unequal, especially near the margin ; inside, under the apex, with two irre- 

 gular callous ridges ; under valve concentrically wrinkled, a disc round the 



