110 
anterior side truncated, with a shallow, oblique furrow running 
near to the hinge line, most deeply defined in the convex 
valve ; basal line nearly parallel ; surface of a sand-colour, 
strongly wrinkled, and slightly and irregularly striated concen- 
trically ; when viewed through a lens presenting the appear- 
ance of shagreen, and feels very rough to the touch ; behind 
the cartilage side one valve turns upwards, and embraces the 
edges of that opposite ; hinge with one broad, very strong, 
thickened, complicated, bipartite, horizontal, tooth-like plate 
in each valve, to which the cartilage is attached, that of the 
convex valve sunk below the level of the hinge line, and in 
the flat valve almost entirely exposed above it; inside white, 
and glossy. 
Found on the Devonshire coast of a large size, but is a very 
local species. 
2. Thracia convexa, pi. XLIV, f. 3. 
Anatina convexa^ First Ed., pi. 11, f. 3; Turton, Biv., p. 
44, pi. 4, f. 1, 2; Mya convexa, Wood, Gen. Conch., p. 92, pi. 
18, f. 1 ; Brown, Ency. Brit., 6th Ed., VI, p. 404; Thracia 
convexa, Leach, MSS., p. 5; Amphidesma convexum, Fleming, 
p. 431. 
Shell subtriangular, very convex, and extremely brittle ; um- 
bones obtuse, placed nearly central, a little inflected, and almost 
touching each other; sides rapidly descending, the posterior one 
rounded, anterior one truncated ; the truncation bounded by 
an elevated ridge, which takes its rise from the beaks, and ter- 
minates on the basal margin, which is a little arcuated ; surface 
of a sand-colour, concentrically wrinkled, obsoletely and irregu- 
larly striated, and very indistinctly granulated ; dentary plate 
obliquely elevated, narrow, with several longitudinal furrows for 
the reception of the cartilage ; inside smooth, white, or pale 
reddish-brown. 
In the adult shell the umbones are so very contiguous, that 
they only permit the valves to open to a small extent, not 
more than half an inch. 
Found on the Devonshire and Welsh coasts, and also in 
Ireland ; and odd valves are frequently met with at Cramond 
Island, Frith of Forth; Turton mentions Paington Sands. It 
is an extremely local species. 
3. Thracia pubescens, pi. XLIV, f. 6. 
Anatina villosiuscula. First Ed., pi. 11, f. 6; Macgillivray, 
Phil. Journ., 1827, ph 1, f* 10, 11 ; Anatina declives, Turton, 
Biv., p. 47 ; Mya declivis, Montagu, pi. 1, f. 2; Amphidesma 
declive, Fleming, p. 432. 
Shell transversely oblong-ovate, compressed, thin ; umbones 
placed to one side; posterior side much rounded; anterior side 
contracted, and truncated; an elevated ridge emanates from 
below the umbones, and terminates at the base of the trunca- 
tion ; one central, flat, transverse tooth in each valve ; external 
surface with a fine pubescent appearance, when viewed through 
a strong lens. 
Found in Dublin Bay, the Dorsetshire coast, and Frith of 
Forth. 
4. Thracia ovata, pi. XLIV, f. 4. 
Anatina ovalis. First Ed., pi. 11, f. 4. 
Shell transversely ovate, subtriangular ; umbones nearly cen- 
tral, very obtuse, and not inflected; sides almost equally round, 
but very slightly truncated on the anterior one ; hinge with a 
narrow, transverse tooth ; surface a little shagreened, which. 
[Myaria. 
however, can only be seen by the aid of a strong lens ; colour 
pale yellowish-white ; inside white. 
I found this shell at Color Cots sands, Northumberland. It 
may be merely an accidental variety of T. declivis. 
5. Thracia distorta, pi. XLIV, f. 7. 
Anatina distorta. First Ed., pi. 11, f. 7; Turton, Biv., p. 48, 
pi. 4, f. 5 ; Mya distorta, Montagu, p. 42, pi. 1, f. 1 ; Amphi- 
desma distortum, Fleming, p. 432. 
Shell rather convex, transversely subovate, thin, fragile, 
rugose, and distorted, particularly towards the base of the 
valves; umbones straight, placed considerably to one side; 
shorter side well rounded, the other considerably acuminated ; 
hinge with a broad, triangular, slightly hollow tooth in both 
valves; inside white. 
Found at Plymouth, South Devon, and at several places on 
the Irish coast. 
6. Thracia truncata, pi. XLII, f. 28. 
Anatina truncata, Turton, Biv., p. 46, pi. 4, f. 6. 
Shell convex, cuneiform, subquadrangular ; anterior side des- 
cending in an acute angle from the umbones, which are situate 
near to that side; posterior side long, with the superior or hinge 
line very flat, and abruptly truncated; basal margin nearly 
parallel; surface pale yellowish-brown, transversely striate; teeth 
projecting somewhat obliquely inwards. 
Found in the interior of rocks at Torbay. 
7. Thracia brevirostra, pi. XLIV, f. 11, 12, 13, 14. 
Anatina brevirostra. Brown, Edin. Journ. Nat. and Geo. 
Science, I, p. 11, pi. 1, f. 1, 2, 3, 4; Ncera brevirostra. Gray. 
Shell very convex, transversely oblong-ovate ; posterior side 
rounded; anterior side abruptly tapering to an acuminated, 
abbreviated beak; umbones small, pointed, and slightly inflected 
towards the anterior side ; exterior surface covered with a rich 
fawn-coloured epidermis, with a slight metallic lustre, beneath 
which the shell is provided with nearly obsolete, transverse 
stricB ; hinge with one large, elevated, recurved, cardinal tooth 
in the right valve, which fits under the edge of the superior 
margin in the left ; cartilage fixed in central pits beneath the 
umbones; inside pale purple, darker towards the extremities; 
margins plain. Length three-eighths of an inch ; breadth up- 
wards of half an inch. 
This interesting species was discovered in the Frith of Forth, 
by James Gerard, Esq.; and I afterwards met with it near Port 
Seaton. It is also said to have been found on the Northum- 
berland coast. 
Genus 38 Lepton. — Turton. 
Shell compressed, transversely elongated, or nearly orbicular, 
equivalve, and slightly inequilateral, gaping a little at the sides ; 
umbones nearly central, and very slightly inflected ; hinge of 
one valve with a central, erect, primary tooth, situate between 
two hollows, from both sides of the hinge emanate a nearly 
straight, transverse rib, lying a little way within the margin, 
upon each of which rests a small tooth-like process, not very 
remote from the hinge, the rib on one of the sides is furnished 
with a small, internal, oblique, spoon-shaped cavity ; the other 
valve is destitute of primary teeth, but with a large, central, 
triangular hiatus for the reception of the tooth of the opposite 
valve ; on each side of which are lateral teeth, cleft their whole 
MOLLUSCA. 
