376 MOLLUSCA. SESSILIA. Discina, 
gin not waved ; hinge patulous, short — Anomiae striata, Ure^ Ruth. 314. 
t. xiv. f. 13, 14. — A. resupinatus, Mart. Derb. t.-xlix. f. 13, 14. — In Carboni- 
ferous Limestone. 
16. S. Marumi,— .Transversely oval, convex, decussatedly striated; the 
longitudinal striae 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 — CTVe, Ruth. 313. t. xiv. f. 12. — Carboniferous 
Limestone. 
18. S. exaratus. — 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.” — 
( Sowerhy.) 
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.— /S'ower. 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. ostreoides . — Upper valve with fine longitudinal ribs, 
crossed by concentric wrinkles. 
Lamark, Hist. pt. i. 236. — Orbicula Norvegica, G. B. Sowerhy, Lin. 
Trans, xiii. 468. t. xxvi. f. 2.— Habitat uncertain. 
Length about i^gths, breadth x*gths 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 
