. Lysianassa. 
CONCHIFERA. 
229 
Genus LXIII.—'TIIRACIA.— Leach. 
Shell very thin, transverse, inequivalve, inequilateral, one 
valve usually more convex than the other ; beaks generally 
obtuse, and sub-central; hinge with a broad, transverse, fre¬ 
quently thickened tooth in the centre, in which the cartilage 
is situate ; surface covered with a very thin epidermis; two 
well-marked but dissimilar muscular impressions in both 
valves; pallial impression interrupted by an arcuated sinus 
at the posterior side, which is truncated. 
I. Thracia oblata.— The 13rought-up Thracia, pi. 
XCIII. figs. 2, 3. 
Lulraria (?) oblata. Sowerby, VI. p. 66, pi. 534, 
fig. 3. 
Transversely oval, compressed; both sides obtuse and 
slightly bent; beaks prominent; both sides obtuse ; surface 
small; near the posterior side a small keel ; pallial impres¬ 
sion with a deep sinus. 
The London Olay., Pegwell, Herne Bridge, and Bognor. 
2. Thracia depressa. —The Depressed Thracia, pi. XCIII. 
lig. 5. 
My a depresm. Sowerby, Y r . p. 1.9, pi. 418. 
Obovate, compressed, very slightly gaping, anterior side 
shorter than the other; hinge-line straight and depressed ; 
ligament external and short; beaks prominent and incurved ; 
surface smooth, with many undulating lines of growth ; sub¬ 
stance of the shell thin. 
The Portland Stone, Brill, and Isle of Purbeck, and the 
Kimmeridge Clay, Weymouth and Specton. 
3. Thracia declives. —Bent-Down Thracia. 
F. declivis. Brown, I Hast. Rec. Conch. Brit. p. 109, pi. 
44, fig. 5. 
Transversely oblong ovate; rather compressed and thin ; 
beaks largo, very obtuse, and not quite central, that of the 
larger valve with a hiatus for the reception of the beak of the 
other valve, not to prevent the opening of the shell; posterior 
side rounded ; anterior side truncated, with a shallow, oblique 
furrow near the hinge line; basal line nearly straight; sur¬ 
face strongly wrinkled, and irregularly striated concentri¬ 
cally. 
The Red Crag, Sutton ; and the Coral Crag, Ramshot. 
4. Thracia dubia. —The Dubious Thracia, pi. XCIII. 
figs. 7,8, 9. 
Transversely ovate; beaks approximate; a flexure from 
the beaks to the base; surface smooth. 
The London Clay, Bognor. 
Genus LX IV. —A N T AT IX A .— Lamarck. 
Shell transverse, free, inequilateral, generally with unequal 
valves ; sometimes gaping at both ends, and in some species 
nearly closed; generally provided with a small accessory 
spoon-shaped appendage, internally, in each valve, to which the 
ligament is attached; connected with this, and also adhering 
to the ligament, is a small irregularly-shaped testaceous inter¬ 
nal process, which serves to assist in strengthening the adlie 
sion between the valves. 
1. Anatina undulata. —The Waved Anatina, pi. XC. 
fig. 30. 
Sanguinolaria undulata . Sowerby, VI. p. 91, pi. 548, figs. 
1, 2. Phillips, Geo. York, I. pi. 5, fig. 1. 
Much elongated transversely ; its width being considerably 
more than twice its length ; thin, convex, rounded before and 
sub-truncated behind ; gaping slightly ; surface with transverse 
undulations, which generally become obsolete towards the 
posterior side ; slightly pcarlaceous within. 
The Calcareous Grit, Malton and Brora; the Oxford Clay 
and Corubrash, Scarborough. 
Genus LXV.— LYSIANASSA .—Man ter. 
Shell thin, transverse, inequilateral, oval, convex, or ven- 
tricose; gaping at both sides ; surface ribbed ; those on the 
cardinal margin anteriorly bent backwards, and the ribs on the 
posterior side bent forwards, and radiated on the middle of the 
back ; beaks sub-central; hinge unknown. 
1. Lysianassa anguilifera.—T he Angled Lysianassa, pi. 
XCII. fig. 32. 
My a anguilifera . Sowerby, III. p. 46, pi. 224, figs. 6, 7. 
Transversely elongated; width nearly thrice its length ; 
gibbosc; auterior side broadest and gaping; posterior side 
being small; surface with obtuse angularly bent ridges, which 
extend beyond the central portion, many of them reaching the 
front without bending; beaks a little produced, but obtuse. 
The Fuller's Earth, Smallcomb ; Bath and Bathford Hill. 
2. Lysianassa literata.—T he Lettered Lysianassa, pi. 
XCII. fig. 34. 
M . literata. Sowerby III. p. 45, pi. 224, fig. 1. 
Transversely elongated; its width more than twice its 
longtli; sub-equilateral, convex; surface smooth, with obtuse 
angularly bent ridges, their angles upon the central portion 
in a longitudinal direction ; substance of the shell thin. 
Coral Rag, Malton ; Cornbrash, Scarborough; the Inferior 
Oolite, Coldmoor, Yorkshire. 
3. Lysianassa v. script a. —The Letter V. Lysianassa, 
pi. XCII. fig. 33. 
M. V. scripta. Sowerby, III. p. 46, pi. 224, f. 2, 3, 4, 5. 
Transversely elongated, sub-equilateral, convex, smooth, 
with obtuse, angularly bent ridges upon the central portion; 
angles of the ridges acute, in an oblique direction. 
Distinguished from L. anguilifera , by the oblique direction 
of the angles of the ridges, which are likewise more acute. 
There is another variety which has an oblique elevation bounding the 
anterior side. 
The Kelloways Rock, Wiltshire ; the Cornbrash, Bedford ; 
and the Iuferior Oolite, Claydon and Brora. 
4. Lysianassa iuiombifera.—T he Rounded Lysianassa, 
pi. LXI.*** fig. 28. 
• Ovatoly trapeziforni; narrow in front; obliquely truncated 
and gaping posteriorly ; beaks sub-central; the ribs angulated, 
truncated, and bent backwards. 
The Lias, Antrim, Ireland. 
