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

108 MOLLUSCA. [MACTRACEA. Section II.-Lateral teeth st1·iated; the sliell stro11g. 4. MACTRA SOLIDA, pi. XLI, f. 3, 4. Mactra solida, First Ed., pi. 15, f. 3, 4; Montagu, p. ~2 ; D Ir PI 6 1 and 126; Turtoo, Div., p. 67; Flemmg, onovan, , · p. 426. Shell subtriangular, strong; sides nearly equal; umbones almost central; lateral teeth large, prominent, and strialed; surface white, or yellowish-white, with a few concentric ridges. General lenglh an inch and a half; breadth an inch and three- qu11rter~; although it not unfreq~ently attains thc size of our figure. Not unfrequent on many of the saudy shorcs of Britain and Ircland ; it lurks a few inchcs below the surfacc. 5. MACTRA TRUNCATA, pi. XLI, f. 5. Mactm t1-uncata, First Ed., pi. 15, f. 5 ; llfontagu, Sup., p. :!4; Turton, Biv., p. 68; Fleming, p. 427; l,{actrn s11bt1·1mcata, Dono1•an, IV, pi. 126. Shell triangular, very strong, thick, and nearly smooth, but with a few remole, trausverse, nearly obsolete lines of growth ; sides nearly equal, considerably flattened, and truncated; um- boncs rather prominent; colour ycllowish-white. Ordinary length an inch and a half; breadlh an ind1 and three-quarters. Some Conchologists consider this as a mere modification of .M. sol-icla, but we possess it from the smallest size to the adull, and the same form is preserved in all its stages. It cli lfers also from the latter species in lhe pa\lial sinus being broader, ancl does not run so far into the shell; it is invariably s tronger. Plentiful in the Frith of Forlh, of a Jarge size ; a11d is not un- frequently met with on many of the British and lrish coasts. G. MACTRA SUDTRUNCATA, pi. XLI, f. 7. 1lfactrn subti-uncata, First Ed., pi. 15, f. 7; Montagu, p. 93; lb., Sup., p. 34, pi. 27, f. l ; Turlon, Biv., p. 70 ; Fleming, p. •127; Forbes, P· 48; illactra St1dto1·1tm, Pennant, pi. 52, f. 42. Shell subtriaugular, strong, moderately convex; umbones l:irgc, prominent, placed considerably to one sicle, and nearly ~lraight; the shorter side rounded, the other produced, ancl a liltlc pointcd; thc anterior side so much ílattened below thc umhones, that it prcsents an clong:ited, cordiform shape, when \'iewed straight. in front ; externa] surface ycllowish-white, with pretty strong, trans\'erse striro, ancl somelimes with inequidis- tant, strongly marked lines of growth; inside smooth, yellowish- white. Length rarely exceeding three-quarters of an inch; hreadth nn inch. Common on most snndy shores. 7. l\facTnA STRtATA, pi. XLI, f. 10. ll[act·rn st?-iata, First Ed., pl. 15, f. 10 ; Brown, Ency. Brit., VI, p. 471. Shell lrans\'crsely elongated, rather strong; umbones small, subcentrnl; anterior side subclepressed, ancl rounded ¡ posterior side elongatecl, ami subo\'alc, its superior line gcntly arcuatecl, as well as the basal margin; surface brownish-yellow, coverecl with strong, trans1·erse, cquidista11t striro; inside smooth, white. This species bcars a strong simi litucle to M. s11bt1·1mcata, but cliffcrs in the posterior sicle being lcss acute, the umboncs being much smaller in proportion lo the size of the shell, in thc striro assuming ncarly the charact er of ribs, nnd in the shell being considerably larger. I procured this species in Lough Strangford, County of Down, Ireland. 8. MACTRA ELLIPTICA, pi. XLI, f. 6. jJfactra clliptica, First Ed., pi. 15, f. 6 ; Forbe~, p. 48. Shell transversc, rnther thin, elliptical, or slightly subtrian- gular; sidcs nearly equilateral, ancl slightly ~ounded ;. umbon~s nearly central, very much depressed; cardmal margm prom1- nent; surface coverecl with a thin, yellowish-brown, glossy epi- dermis, bcnealh which the shell is nearly smooth, or obsolctely striated transverscly, which, however, can only be seen by thc aid of a strong lens; teeth similar lo thc other species of this scction, but much smallcr in prc.portion to the size of the shcll; inside smooth, white, ancl glossy. This shcll was mistaken for the young of 111. solida, but its more elliptical form, its epidermis, ami thinness, at once distin- guish it from that spccics; which characlers it preserves in ali stages of growth. Found frequently in the Frith oí Forth, and can readily be procured at Crnmond Island, at low water. F orbes found it on the norlh coast, Isle of Man. GENUS 35.-MACTR!NA~Brown. Shcll subtriangular, equivalve, nearly equilateral; umbones nearly central¡ left valvc with a slrong, central, triangular, slightly bifid tooth, which locks into a corresponding pil in the opposite valve; on each sido oí which are triangular, transverse pits, for thc reception of two small, depressed, cardinal teeth in thc right \'alve; ligament. externa]¡ two strong muscular impres- sions in each valve; pallial impression entire. J. MACTR!NA TRIANCULARIS, pl. XL, f. 25. 1lfact1·i11a t,,ia11gttla1·is, First Ed., pl. 16, í. 25 ; Brown, Conch. T ext Ilook, p. 140, pi. 18, f. 30; Gooclallia tria11gularis, Turton, Biv., p. 7í, pl. 6, f. 14; Fleming, p. 429; Forbes, p. 48; ltlactra tria11g-ulm·is, Montagu, p. 99, pi. 3, f. 5. Shcll elongatcd, subtriangular, strong; sicles a li ttle unequal; umbones prominent, obtuse; white, subopaque, smooth ; hingc with a large, bifid, central, strong, cardinal l ooth, in one vnlve, and a pit on each side; opposite vah-e with a triangular, central pit, for the reccption of the tooth in the othcr vah-e, and a small tooth on each sido of the pit, which lock inlo the cor- r esponding pils; insidc rather dul\ white; the margin strongl~· crenatcd. Length one-eighth of an inch ; brcadth somewhat less. Found in sand at Falmouth Harbour ; Portmarnock, I reland; and Dunbar, Scotland ; very raro; ami on the Manx coast, by Profcssor Forbes. 2. MACTRINA MINUT!SSIMA, pi. XLII, f. 25, 26. Gooclallia mimllissima, Turton, Biv., p. i7, pi. 6, f. 15; Fle- ming, p. 429; Forbes, p. 48; lilactra minutissima, 1\-lontngu, Sup,, p. 3i. Shell rathcr strong, subtriangular, white, ancl almosl smoolh; umbones prominent, nearly central ; sides l'ery flat; basal mar- gin nearly parnllel, but gently rounclecl al each cxtremity; hinge strong; lwo cardinal teelh in one valve, with an intermcdiatc, prelly largc, central cn1·ity for the rcception of the largo, cardi- nal, triangular tooth with which the opposite l'all'e is prol'ided; insidc smooth, glossy ; margin plain. Somewlrnt lcss than n quarter of an inch in lcngth.