CLASS SECOND. 
CONCHIFERA; 
Animals soft, without articulations, destitute of a head or 
organs of vision, and always fixed within a BIVALVE shell; 
provided with external branchie, a simple circulation, and an 
unilocular heart. 
All the species are aquatic, living either in the sea or fresh 
water. None of the animals have an internal shell. The body 
is invariably soft, and the mouth is situated near the left side of 
the hinge. 
Sus-Division I. 
Ligament none or unknown, or in its stead a tendinous chord, 
which supports the shell. 
ORDER I.—MONOMYARIA. 
Animals provided with but one muscle of attachment, or ad- 
ductor muscle, which leaves one subcentral muscular impression 
inside of each valve. 
Famity I.—Bracuropopa. 
Shell bivalve, adhering to extraneous marine bodies, either 
by the shell itself, being in contact with them, or attached by 
a tendinous chord. Shells not quite equivalve, and open by a 
hinge. 
Genus 1.—TEREBRATULA.—Bruguiere. 
Shell inequivalve, equilateral, generally trigonal and gibbous; 
attached by a short peduncle to extraneous marine bodies; the 
larger, or upper valve, with a projecting umbo, frequently bent, 
and perforated at its apex, or notched at its inner edge, and 
having a small curved tooth on each side of its hinge, which fits 
into a corresponding pit in the opposite valve; the inside of the 
smaller valve is provided with two slender testaceous processes, 
which are sometimes simple, short, and recurved, at others con- 
siderably elongated, branched, bent in various directions, and 
anastomosing for the most part; sometimes they are situate 
near the centre of the valve, and in other instances are united 
by their points to the shell; these usually emanate from each 
side of the hinge; both valves are provided with two nearly 
obsolete, muscular impressions, but sometimes they are strongly 
developed; those of the larger, or perforated valve, are oblong, 
central, and close to each other; in the smaller valve they are 
triangular, with their angles rounded, also nearly central, but 
more distant than in the other valve. 
1. TEREBRATULA cRANIUM, pl. XXII, f. 10, 11, 12. 
Terebratula cranium, First Ed., pl. 34, f. 10, 11, 12; Miiller, 
Prod., p. 249; Ib., Zool. Dun., pl. 84, f.1; Fleming, Phil. 
Zool., II, p. 498, pl. 4, £45 Ib., Brit. An, p. 368; Terebra- 
OR BIVALVES. 
tula vitrea, Fleming, Edin. Ency., VII, p. 96; Montagu, Linn. 
Trans., p. 288, pl. 13, f.2 B; Anomia cranium, Brown, Ency. 
Brit., VI, p. 422; Turton, Biv., p. 236. 
Shell ventricose, front margin slightly truncated, semitrans- 
parent, brownish-white, with the external surface finely and 
delicately shagreened, which can only be seen by the aid of a 
strong lens, and slightly and irregularly wrinkled concentrically ; 
larger valve with bifid lateral teeth; those of the smaller valve, 
with a small, horizontally projecting tooth, from which emanate 
two projecting processes, upwards of three-fourths across the 
shell; provided with a simple peduncle. 
Found in deep water at Bressay, Zetland, by Dr. Fleming; 
and a single specimen was dredged alive in Dublin Bay, which 
is now in the Museum of the Dublin Society. 
2. TEREBRATULA AuRITA, pl. XXII, f. 13, 14, 15. 
Terebratula aurita, First Ed., pl. 34, f. 13, 14, 15; Fleming, 
Phil. Zool., II, p. 498, pl. 4, f. 5; Ib., Brit. An., p. 369; Tere- 
bratula costata, Lowe, Zool. Journ., II, p. 105, pl. 5, f. 8, 9. 
Shell rather thin, semitransparent, and compressed; narrow 
at the summit, suddenly widening as it descends, and termi- 
nating in a well rounded basal margin; upper valve flattish, 
semicordate, and inequilateral; beak slightly produced, a little 
rounded, and horizontally truncated, for the reception of the 
perforation, which is large, and completed by the pointed umbo 
of the lower, or smaller valve; lower valve somewhat rounded, 
a little depressed, with a slight central elevation; both valves 
covered externally with regular, longitudinal, divergent, some- 
what scabrous ribs, which are interrupted by a few irregular, 
inequidistant lines of growth, producing a scaly or yaulted ap- 
pearance ; margin of the valves regularly rounded and toothed, 
but destitute of any sinuosity; colour an obscure reddish-brown 
towards the beaks, which becomes less intense as it diverges 
towards the margins; inner surface minutely punctated, pale 
yellowish, or cream-coloured white; peduncle short, consisting 
of numerous, unequal, tubular filaments, attached to a compli- 
cated tendino-muscular apparatus, and chiefly to the lower 
valve. Length somewhat more than three-tenths of an inch; 
breadth rather less. 
Discovered by M. J. Berkeley, Esq., attached to the under 
side of a rock, on the beach near the Custom House, Oban, at 
a very low tide. A specimen was sent to me, from the same 
locality, by Captain Carmichael; and Dr. Fleming found it in 
Ullapool, Loch Broom. 
3. TrREBRATULA PsITTACEA, pl. XLVI, f. 2, 3, 4. 
Terebratula psittacea, First Ed., pl. 10,* f£. 2, 3, 4; Turton, 
Conch. Dict., p. 5, pl. 11, f. 42; Ib., Brit. Biv., p. 236. 
Shell oval, convex, of a dark horn-colour; beaks greatly pro- 
duced, and curved; superior margin undulated ; sides abruptly 
turned inwards, depressed, and provided with a few longitudinal 
striae; front margin somewhat indented on both sides, and pro- 
