Illustrations of the recent conchology of Great Britain and Ireland, with the description and localities of all the species, marine, land and fresh water

MACTRACEA.] MOLLUSCA. 105 l. Co1mut,A NUCLEus, pi. XLH, f. 7, S, 9. Corbula nuclcus, firsl E<l., pi. M, f. i, S, !); Lamarck, V, P· •196; Turton, Ili,·., p. 39, pi. 3, f. 8, 9, 10; Corbulii st?·iata, Flcming, p. '125; 11f.1Ja incr¡uivalvis, Montagu, p. 38, pi. 26, f. 7; llfaton and Hackett, p. 40, pi. 1, f. G. Shell subtriangular, strong, thick, opaque, whitc; with an umbcr-brown, rathcr thick epidermis ; undcr vah•c very convex, with a large, tumid, inílecte<l umbo, consi<lerably clevatcd above thc hinge; upper valve ílat, or somewhat concave, \\'.ith a small but acute umbo, ali(! Iittle more than half the s1zc of the other, providc<l with a fcw short, distan!, irregularly divergent strim, which cmanatc from ncar thc central <lisk of thc shell, ami tcrminate 011 the margin; larger valve with one strong, ercct, somewhal recurved tooth, which is received into a socket in the smallcr val\'C; in,i<le smooth, dull white; the margin somewhat flattcncd, an<l that of the larger valve projecting con- siclerably bcyon<l the other, when closcd. This spccics is by no mcans uncommon on most of the coasts of Britain ami Ircland. It attains a largc sizc in the lattcr country. 2. CORDULA OVATA, pi. XLII, f. 32, 33. Corbula ovala, Forbes, p. 53, pi. 2, f. 8, 9. ce Shell ovatacoblong, almost cquilateral, with obsolcte trans- verse strire; white, covcrecl with a brown epidermis, which is worn away al the upper part of the shcll, but bears the traces of regular, transvcrsc strim towards thc margin ; the anterior exlremity is slightly truncatc, the posterior rounded; beaks de- prcssccl; transluceot. ce In form this species resembles the Co1·bula 1·osca, but is more elongatccl lransversely; the tecth are very similar. " Taken from the root of a F1,cus, cast ashore al Ballaugh, !sic of l\'Ian."-Fo1·bes. 3. CORDULA ROSEA, pi. XLII, f. 6. Coi·bula 1·osca, Firsl Ed., pi. 42, f. 6 ; Leach, l\'18S. Shell subtriangular, subovale, subcompressed, its breadth con- siderably cxcecding its length; undcr valvc but a little largcr than thc othcr, its umbo of moderale size; surfacc smooth, covcred with a very thin, palc yellow epidermis, beneath which the shell is of a beautiful roseate hue, with a few short radia- tions of a darker cast, near the umbones; insicle smooth, of a pale rose-colour; margins smooth, ancl glossy. This shell cliffers con:siderably from the young of C. nucleus, in being devoid of the peculiar curve of that shell; in the beaks of the lower valve being much less, and a less disparily in thc size of the upper and under valve; and in being much more compressed. In thc cabinet of Dr. Leach, British Museum, and were drcdged al Falmouth. FAl'>IILY VII.-MACTRACEA. Shells equivalve, frequently gaping at the lateral extremities; ligament situatc inleriorly, or partly externa!. Saction 1-Ligament seen extarnally, 01· double. GENUS 31 -AMPHIDESMA-Lamarck. Shell equivalve, transvcrse, slightly inequilatcral! some_whal ovale, or orbicular; some spccics gaping al thc s1des, w1th a slight posterior fold; cach valvc provided wilh one, or in sorne 20 instances two small, slender, cardinal teelh; and two distinct, clongated, lateral teelh, sit uate near the hinge in onc valve, aml almost obsoletc in the othcr; ligamcnt double, separated from thc cartilage, its externa) portion slendcr, and rather short, the interna) carlilage gencrally longcr and largcr, adherent in both valves to an clongated, obliquc groovc or pit, which varies in lcngth in differcnt species, takes its risc immcdiately within the umbo, and is prolonged within thc anterior lateral tooth; two muscular impressions in cach valvc; pallial impression with a very large sinus. 1. AMPHIDESMA IloYSn, pi. XLII, f. 3. Ligula Boysii, Firsl Ed., pl. 14, f. 3; Lamarck, V, p. 491; Ampliidesma Boysii, Turton, Biv., p. 53, pi. 5, f. 4, 5; lllactm Boysii, l\fontagu, p. 98, pi. 3, f. 7; l\faton and Hackett, p. 72. Shell oval, subcompressed, thin, pcllucicl, glossy, white, mu! nearly smooth; with a fcw remole, obsolete, concentric strire; umbones vcry small, with the ucaks slightly inllccted, situatc nearesl to the posterior sicle_; onc cardinal toolh in cach valve, with a broad, cartilagc cavity; onc valve only provided with broad, clevated, lateral teeth; inside smooth, glossy, ami white; two muscular impressions; the pallial impression wilh a lnrge, nearly obsolelc sinus, running from thc smaller sicle, almost two-thirds across thc vah·cs, and nearly parallcl with thc mnr- gin. Length somcwhat more than half an inch; breadth a littlc more than threc-quart ers. Plentiful on mosl of the British ami Irish coasts. 2. AMPHIDESMA TENUE, pi. XLII, f. 2. Ligula te1mis, Firsl Ed., pi. 14, f. 2; 11Iactm tc1111is, Mon- tagu, p. 572; Ligula tenuis, Montagu, Sup., pi. 17, f. 7; Amphi- desma tenue, Turton, p. 53; Forbes, p. 47; Flcming, p. 433. Shcll subtriangular, compressed, equilnteral, semipcllucid, · thin, whitc; with shallow, eonccnlric wrinkles; umboncs small, eonsiderably produced, placed nearly ce 1 1tral, and nol turning to either sidc ; inside moderatcly smooth, and glossy; pallinl imprcssion interrupted by a broad, conical, ncarly pcrpendiculnr, pointed sinus, reaching nearly lwo-thirds up thc valves; hingc provicled with a cleft tooth, a narrow groovc, and remole, lnmi- nated, lateral teeth, one on each sidc in one vah•e ; thc other with a plain, single toolh, which is received into n cavity in the opposite valve; destitutc of lateral teeth. Lcngth n qunrtcr of an inch ; brcadth somewhal more. Found on the coasls of Hampshire, Dorset, and Devon. 3. AMPHIDESMA PRISMATICA, pi. XLII, f. 5. Ligula p1·ismatica, First Ed., pi. 14, f. 5; Montagu, Sup., p. 23, pi. 26, f. 3; Ampltidesma p1·ismaticum, Flcming, p. 432. Shcll transvcrsely oblong-ovate, ílat, thin, fragile, glossy, pel- lucid, white, exhibiting prismatic reílections; with vcry minute, concentric strim; umboncs very small, inílected, and placed lowards the narrow sidc, which is considerably aeuminatecl, with a slight oblique subtruncation, bclow which it is pointcd; oppo- site sidc finely roundcd; hinge furnished with a horizontal tooth, with a cavily in the centre for the receplion of thc con- necting cartilage, and thc addition of a small, lateral, laminar, remole toolh on each side of thc larger tooth, in one valve, but dcvoid of these in thc other valve. Length threc-eighths of an inch; breadth upwnrds of six-eighths. Found pretty plentifully in the Frith of Forth, the south coast of Dcvon, and by no means rare al Portmarnock, Ireland, ancl other parts of the eoast.