MOLLUSCA. 
109 
Myaria.] 
This species might easily be mistaken for the young of M. 
tnangularis, but will be distinguished from that shell in being 
less angulated, in wanting crenulations on the margin, and its 
breadth proportionably greater ; it is, besides, a considerably 
smaller shell. 
Found on the coast of Cornwall, the Western coasts, and in 
Ireland. Forbes says it inhabits the byssi of Modioli from deep 
water olf Douglas, Isle of Man. 
Genus 36. — Ldtraria. — Lamarck. 
Shell equivalve, inequilateral, thin, transversely ovate or 
oblong; open at both sides; the posterior side generally the 
longer, and always gaping more than the other ; one valve with 
two thin, laminar teeth, one of which is sometimes compound ; 
the opposite valve with three teeth, the central one compound 
in some instances, and the posterior one slender and com- 
pressed ; ligament internal, situate in a deltoidal, oblique, inter- 
nally projecting, spoon-shaped pit, with a prominent margin 
placed next to the teeth in each valve ; two distant, lateral, 
muscular impressions ; pallial impression with a very large 
sinus, lying transversely in most species. 
1. Lutraria elliptica, pi. XLIII, f. 2, 3. 
Lutraria elliptica, First Ed., pi. 12, f. 2, 3; Lamarck, V, p. 
468 ; Turton, p. 6.'> ; Forbes, p. 54 ; Lutraria vulgaris, Fle- 
ming, p. 464 ; Pennant, IV, p. 92, pi. 52, f. 44 ; Montagu, p. 
99 ; Donovan, II, pi. 58. 
Shell transversely oblong-ovate,- thin, compressed ; longer 
side with a shallow groove, emanating from the base of the 
umbones, and terminating on the margin, over which there are 
some irregular strise-like lines, which when the epidermis is 
removed, present the appearance of being scratched by a file ; 
umbones small, placed near to one side; surface with fine, nearly 
obsolete, irregular, concentric strife, or grooves, and irregularly 
wrinkled transversely, these are shallow on the disks, but 
stronger and more decided towards the sides, covered with a 
pretty strong epidermis, of a drab-colour, rarely approaching to 
fawn ; sometimes with a few indications of lines of growth, and 
in some these assume the appearance of nearly obsolete ridges, 
particularly towards the shorter side ; inside smooth, bluish- 
white ; and gaping at both sides. 
Found on many of the British coasts with a sandy bottom, 
especially at the influx of rivers. * 
Fig. 3 is a very thick shell, in proportion to its size, which I 
figured from .the collection of Sir John Trevelyan, Bart., at 
Wallington, Northumberland. 
2. Lutraria Solenoidea, pi. XLIII, f. 1. 
Lutrana Solenoidea, First Ed., pi. 12, f. 1; Lamarck, V, p. 
468; Lutraria ohlonga, Turton, Biv., p. 64, pi. 5, f. 6; Lutra- 
ria Mans, Fleming, p. 465 ; PsammopMla Solenoidea, Leach, 
MSS., p. 6; Mactra Mans, Montagu, p. 101; Donovan, III, 
pi. 140. 
Shell transversely oblong-ovate, greatly inequilateral; um- 
bones small, depressed ; surface with rugose, concentric wrin- 
kles, which prevail most at the posterior side, covered with 
an opaque, dark brown, thick, dusky epidermis, sometimes 
of a reddish tinge ; hinge provided with one flattened tooth, 
which is grooved on the fore part, and locks between two 
2 E 
in the opposite valve, the smallest of which is cleft ; the car- 
tilage pit is large and triangular; inside smooth, white, with 
an elevated, transverse ridge, situate on the upper side of the 
posterior muscular impression ; gaping considerably at the pos- 
terior side. 
An extremely local species, but is said to be not uncommon 
at the influx of the river between Truro and Falmouth, in 
Cornwall ; and has been found on the Dorset coast. 
3. Lutraria compressa, pi. XLIII, f. 4. 
Lutraria compressa. First Ed., pi. 12, f. 4; Lamarck, V, p. 
469; Listema compressa, Turton, Biv., p. 51, pi. 5, f. 1, 2; 
Abra compressa, Leach, MSS., p.6; Amphidesma compressum, 
Fleming, p. 432; Mactra Listeri, Gmelin, p. 3261 ; Mactra 
compressa, Montagu, p. 96 ; Tellina plana, Donovan, II, pi. 
64, f. 1. 
Shell transversely subovate and subtriangular, thin, brittle, 
much compressed ; umbones not quite central, and rather ob- 
tuse ; anterior side well rounded ; posterior side a little longer 
than the other, and slightly acuminated ; external surface of a 
dull yellowish-white, covered with pretty strong, transverse 
strise-like wrinkles; cartilage cavity large, triangular; primary 
teeth small, a single one which locks into a cleft tooth in the 
opposite valve; inside smooth, white, and rather dull; pallial 
sinus very large, occupying nearly a half of the interior surface ; 
margin plain. 
A common species on most of the British coasts, and prevails 
at the mouths of rivers. 
Section IV Crassipedes. 
The mouth united in front, or partly so ; foot thick, and 
situate posteriorly; shells gaping when closed. 
Family VIII — Myaria. 
Shells with a broad, spoon-like tooth in one or both valves ; 
gaping at both extremities ; in most instances with an external 
ligament and internal cartilage. 
Genus 37.— Thracia. — Leach. 
Shell very thin, transverse, inequivalve, inequilateral, one 
valve usually more convex than the other ; umbones generally 
obtuse, and subcentral ; hinge with a broad, transverse, fre- 
quently thickened tooth in both valves, and an obliquely trian- 
gular pit in the centre, in which the cartilage is situate; surface 
covered with a very thin epidermis ; two well-marked, but dis- 
similar muscular impressions in both valves ; pallial impression 
interrupted by an arcuated sinus, at the posterior side, which is 
truncated. 
1. Thracia declivis, pi. XLIV, f. 5. 
Anatina declivis. First Ed., pi. 11, f. 5; Anatina puhescens, 
Turton, Biv., p. 45, pi. 4, f. 1, 2; Thracia declivis, Leach, 
MSS., p. 5; Mya puhescens, Montagu, p. 40 ; Donovan, II, pi. 
82; Amphidesma convexum, Fleming, p. 431. 
Shell thin, brittle, transversely oblong-ovate; umbones large, 
very obtuse, and not quite central, that of the larger valve with 
a hiatus for the reception of the beak of the other valve, and 
to permit the opening of the shell ; posterior side rounded ; 
