CLASS SECOND. 



CONCHIFERA; OR BIVALVES. 



Animals soft, without articulations, destitute of a head or 

 organs of vision, and always fixed within a bivalve shell ; 

 provided with external branchiae, 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. 



Sub-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. 



Family I. — Brachiopoda. 



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, pi. XXII, f. 10, 11, 12. 



Terebratula cranium, First Ed., pi. 34, f. 10, 1 1, 12; Miiller, 

 Prod., p. 241) ; lb., Zool. Dun., pi. 84, f. 1 ; Fleming, Phil. 

 Zool., II, p. 498, pi. 4, f. 4 ; lb., Brit. An., p. 368 ; Terebra- 



tula vitrea, Fleming, Edin. Ency., VII, p. 96 ; Montagu, Linn. 

 Trans., p. 288, pi. 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, pi. XXII, f. 13, 14, 15. 

 Terebratula aurita, First Ed., pi. 34, f. 13, 14, 15; Fleming, 

 Phil. Zool., II, p. 498, pi. 4, f. 5; lb., Brit. An., p. 369; Tere- 

 bratula costata, Lowe, Zool. Journ., II, p. 105, pi. 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 vaulted 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. Terebratula psittacea, pi. XLVI, f. 2, 3, 4. 

 Terebratula psittacea, First Ed., pi. 10,* f. 2, 3, 4 ; Turton, 

 Conch. Diet., p. 5, pi. 1 1, f. 42 ; lb., 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 

 stria;; front margin somewhat indented on both sides, and pro- 



