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

ARCACEA.) MOLLUSCA. 85 Sectioa 11 .-Sltclls subo1·bic11{(1)·. 5. Nucu1.,\ MAIIGAIIITACEA, pi. XXXIII, f. 12. Nucul<t 11w1-garilclcca, First Et!., pi. 25, f. 12; L:unarck, VI, pt. 1st, Jl· 59; ForhC's, p. 43; Nurnla nuclcus, Turlon, l3iv., p. 1 iG, pi. 13, f. -1 ; A1·ca ·1mclc11s, Pcnnant, IV, p. 217 ; Monlagu, p. 1-11 ; Donornn, II, pi. (3:3. Shcll thick, inílatcd, oblic¡ucly orntc, slightly subtrigonal; umboncs rnthcr promincnl, placed nearest Ihe posterior side; beneath thcm a conlifonn clcpression ; colour olive, of various shades in diffcrcnl incli\'icluals, ali(! very glossy; with numerous, concentric, ucarh· obsolcte wrinklcs, crossed by numerous, fine, interrupted slri::c; inside of a glossy, highly nacrcd silvery white; hinge angular, with numerous, upright, sharp teeth, extending considerably aboye the hingc lincs; margin minulely crenulated. Length half an inch; brcadth somewhat more. Founcl on the De\'Onshire, ,velsh, and Yorkshire coasts; also in many parls of Scotland; Dublin Bay, Portmarnock, Bray, and the Downshire coast, Ircland. f>, NucuLA ARGENTE,1., pi. XXXIII, f. 14, 15. iYuculct U1'{J1mlee1, Firsl Ed., pi. 25, f. 14, 15. Shell oblic¡uely ovale, very glossy, ancl smooth ; colour oliva- ceous; umbones placed much to the posterior side, with a cordiform depression beneath; inside g"lossy, silvery whitc; hingc with lwelrc rathcr slrong, regular, upright teeth; margins with very fine crenulations. Lcngth and brcadth not quite a t enth of an inch. One valve only of this shcll was discovercd at Dunbar, by General Ilingham, and is in his cabinet. It has ali thc appcar- ancc of the fry of N . 11ta1'.4'cti·itacca, but diffcrs from it in thc following particulars, viz.: in its subovatc form; having no lon- gituclinal stri::c; hinge line gradually curvcd, and not triangular, as is N . mcn-gcll'itacect; ligamcnt pit in a linc with thc teeth, all(l does not projcct bcyond them; and thc tccth are lcss numerous. 7. Nuc uLA TENurs, pi. XXXIII, f. 13. 1.Vuc11lct tc1mis, First Ecl., pi. 25, f. 13; Turton, Bi,·., p. 177; Arca tenuis, Montagu, Sup., p. 56, pi. 29, f. l. Shcll somewhat ovate, ancl con\'ex, smoolh, and very glossy ; of a pale olivaceous colour, with a few concentric, ncarly obso- leto wrinklcs; umbones rathcr small, prominent, rcllectcd, and placed nearest the posterior sicle, with a slight cor<liform dcpres- sion under thcm; inside smooth, white, and somewhat nacrccl; margin thin, cnt\rc, ami divcsted of crcnulations ; hinge with about sixtecn elel'aled, imbricated teeth, ten on lhc onc side of the cartilagc pit, ami six. on the othcr; cartilage sockcl pro- jecting inwards. Lcngth no! a quarlcr of an inch; brcadth a quarler. Found in the Frith of Forth; the cstuary of thc Clydc; and the coast of Downshire, Ircland. GENUS 5.-PECTUNCULUs.-Lamarck. Shell orbicular, subec¡uilateral, wilh the vah·cs closc; umbones nc:ir to cach other, :ind scparated by a narrow facct, or arca; hinge semicircular; tceth numerous, arcuatecl, oblic¡uc, serraled, placed in two rows, onc on cach side of the mnboncs, ancl scpa- ratcd by a small triangular disk in cach valvc, which contains thc ligamen!, thosc of the oppositc valves altcrnatcly lock betwccn cach other, ancl bccoming ncarly obsolct e lowards the y umboncs; lwo lateral, strongly markccl, distan!, umscular im- prcssions, which are united by an interruptcd pallial impression; ligamcnl CJxlcrnal. l. PECTUNCULUS PIL0SUS, pi. XXXIII, f. 1 o, 1 l. P cctw1culus pilosus, Firsl Ecl., pi. 25, f. 1 O, 11 ; Lamarck, VI, pt. 1st, p. 49; Turto11, Dh·., p. 172, pi. 12, f. 2; Flcming, p. 400; Forbcs, p. 42; Pccl!mculus 1111datus, Turton, 13iv., p. 173, pi. 12, f. 3, 4; Ana pilosa, Montagu, p. 13G; Ib., Sup., p. 53; Maton and Hackett, Linn. Tr., VIII, p. 94, pi. 3, f. 4. Shell orbicular, strong; surface palc rcddish-brown, or whitc; with zigzag, angular, s tripcs of dark chestnut, or reddish-brown, frcquently of a llesh-colour in young shells, with fine, longitu- clinal strire, ancl trans1·ersc, irregular wrinklcs; aboye which thc surface is col'ered with a clark brown, pilous epidermis, which is generally extrcmely thin, or none, near thc nmboncs, ancl lhicker ami longcr towards thc margins ami base of the l'ah·cs ; umbones large, central, ancl roundcd, inclining slightly towards cach other, and scparated by a polygonal, clark blackish-brown aren; insidc white, or slightly tinged with purplc ncar oue side; margin strongly creitated. Diamctcr two inchcs mul n half, sometimcs more. In the young condition the surface is distinctly dccussalccl, but thc transvcrsc stri::c bccome obsolctc as they adrnncc in growth. The P. decussatus of Turton is mcrcly the young of this species. Found on thc soulh coast of Del'Onshirc, ,:i.reymouth, nnd thc Kenlish coast. Professor Forbes dredged it of a largc si1.c in the Il'ish Channel, off the Manx coast, whcrc it is plentiful. H e particularises thc coast off Douglas Head, as being a locality wherc it is abundan!. 2. P ECTUNCUI,US GLYCIMERIS, pi. XXXIII, f. 8, 9. P cctm1culus G(,¡ci111e1·is, First Ed., pi. 25, f. 8, 9; Turton, Biv., p. 171, pi. 12, f. 1 ; A1·ca Glgci11ic1·is, l\faton nnd Hackell, Linn. Tr. VIII, p. 93, pi. 3, f. 3. Shcll orbicular, con\'ex, thick, slrong ; umbones dislant, round, and pointing lowards each other; hingc line with a poly- gonal arca of a decp brown colour, but not striatc; wholc sur- face of a palc ycllowish-white, with ncarly obsoletc, widc-set, longitudinal, ami transverso stri::c, irregul:irly and rcmolcly spolled with yellowish-brown ; covcrcd with a dark, subpilous epidermis; margin strongly crenated, and acule at thc cdgc; cardinal tecth transvcrse, about ten in number. Diameter two inchcs and one-eighth, ancl upwards. Distinguished from the P. pilosus by being much more ven- tricosc, in thc tccth being fewcr in number, and with thc epi- dermis less pilous than in thal shell. Found on thc Western coasts, Cornwall, and British Chan- ncl, but is very rarc. GENUS G.-AncA...-Linnreus. Shell transvcrse, or subequivalve, incc¡uilatcral, trapeziform, or subquadratc; slightly vcntricose; sorne species grcatly ven- tricose; generally angular al both cnds of the hinge line, much roundcd in sorne spccies; umbones small, rcmote, scparatecl by thc arca, to which thc externa! ligamcnl is affixcd; hinge linc rectilinear; tceth numerous, small, serratcd, closc-set, altcr- nately inserted in thc opposile valvcs; two lateral and distnnt muscular impressions ; ligamcnt ex.terna!.