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

78 MOLLUSCA. [NAYADES- 2. Moo10LA Grnusu, pi. XXVII, f. 7. Mudiola Gibbsii, First Ed., pi. 29, f. 7; Leach, MSS., p. 11 ; lb., Miscell., II, p. 34, pi. 72, f. 2; Turton, Div., p. 200, but not thc figure; Fleming, p. 413. Shell somewhat triangular, compressed; beaks roundcd; pos- terior sidc very short; anterior sidc very long; basal margin a littlc concave; externa! surface regularly and transversely stri- atcd, covered with a thick, umber-brown epidermis, which extcnds into foliation$ at the lines of growth; theso are pro- longed into filamcntary processes, each of which is pectinated or notched down both sidcs, producing a beardcd appearance; inside of a ycllowish-whitc. Length about two inches. This spccies is much more triangular than the young of JJ/. ¡1apuana, and will ea.sily be distinguished by the beard being simple in that species, whilc it is serratcd in the present. Tur- ton has complctcly mistaken thc figure of this spccics, and has givcn that of JJI. marmo1·ata in its steacl. Founcl on the Western coasts of England. 3. MODIOLA DISCREl'ANS, pi. XXVII, f. 8. Modiola disc1·epa11s, First Ec!., pi. 29, f. 8; Lamarck, VI, p. 114; Forbes, p. 44; Fleming, p. ,113; JJfytilus disci-epans, Montagu, p. 169; lb., Sup., p. 65, pi. 26, f. 4; Brown, Ency. .Brit., p. 424 ; lJl!}tilw; discoi·s, /3, Maton ancl llackett, p. 111, pi. 3, f. 9. Shell thin, suboval, compressed; externa! surface clivicled into three compartments, the posterior and anterior sidcs longitu- dinally ribbed, the mic.ldle arca slightly wrinkled; umbones obtusc and blunt, placed considcrably towar<ls the posterior side, which is much narrower than thc broad ami roundcd ant.crior onc; wholc surfoce covercd with a thick, black epider- mis; insidc whi1e, exhibiting iridesccnt reílcctions. Usual lcnglh al broaclcst part somcwhat more than half an inch ; breadth an inch and a quartcr. ll has bccn found two inches in breadth. Found on most of lhe British ami Irish coasl$, 4. l\foo101.A MAIIM0RATA, pi. XX VII, f. JO. 1/locliol<t discon, Firsl Ed., pi. 29, f. 1 O; Flcming, p. 413 ; Turton, Di1·., p. 201, pi. 15, f. 4, 5; 111odiola 111arnio1·atus, Forbcs, p. '1<1; 11/¿¡tilus disco1·s, Pcnnant, IV, p. 2,10; Montagu, P· 167; .Maton ami Hackctl, p. 111, pi. 3, f. 8; Brown, Wer- ncrian l\lcm., II, p. 515; Ib., Ency. Brit., p. 42,1. Shell vcry convex, somcwhat cordiform; thc po,terior and anterior sidcs with about cighteen fine, longitudinal ribs, broadcr ami slronger on thc post.crior sidc; the micldle arca plain, or slightly wrinklcd lransverscly; umboncs large, promi- nent, obtuse at the point, lurncd to onc sidc, ancl sitnatc ncar the posterior sidc, which is roundecl ; anterior sidc bcakcd, and slightly constrictcd; externa! surface co1'ercrl with an olirn- grccn, glossy epidermis, bcneath which thc shell is whitc, oftcn mottlcd with pink or palc red; insidc whi1c, tingcd wilh pink; margin providcd wilh crcnulalions, which correspond with thc exterior surfacc, which is ribbcd, thc other portions plain. Or- c.linary lcngth thrce-cighths of an inch; brcadth fil·e-cighths; sometimes, howe1·cr, although rarely mcl with, se1·cn-eighths in breadth. . This spccies is common on ali thc British coasts, burrowing 111 the roots of Alga:, ami vcry often founcl lodgcd in thc sub- stance of the AsC'icli<i 1 lc11tula. This is nol lhc JI/. cliscol'S of Lamarck, which is a forcign spccies, and very diffcrent from our shcll; and, thcrcforc, I cor- dially approvc of thc namc givcn to it by my friend Profcssor Forbes. Young shclls of thc JJ/. clisc,•cpans have been confoundcd with this spccics, but thc following distinctions will shcw that lhcy are widcly cliffcrent. Thc JJ./. disco1·s is vcry convex, ncarly as thick as broad, an<l pointcd at thc anterior side; thc posterior sidc with about cighteen ribs; whilc thc M. clisc1·e- pa11s is deprcsscd, broad and roundcd al. thc anterior siclc, ami wilh only cight or ninc ribs on thc posterior sidc; thc epider- mis is also more clull. 5. l\foDIOI.A PRIDEAUXIANA, pi. XXVII, f. 9. Moáiola P,·iclcau.i·iana, Firsl Ed., pi. 29, f. 9 ; Lcach, Zoo!. Misccll., II, p. 34 ; lb., MSS., p. 11. Shcll subtransvcrse, a littlc comprcssecl; striatcd from thc umbo to thc basal margin, with tran$1'Crsc, almost cquidistant wrinklcs; colour palo saffron•yellow cxtcrnally, ancl whitc intcr- nally, with a slight mctallic lustre. Lcngth about an cighth of an inch; breadth a quarter. Foun<l on thc Devonshirc coast, by Mr. Prideaux. 6. l\fou!OLA RII0MDEA, pi. XXXIX, f. 17. 1Wodiola 1·hombea, Berkeley, Zoo!. Journ., III, p. 229, Sup., pi. 18, f. l. Shell thin, subrhomboidal, gibbous, with transverso, subcrc- nulatcd plications, ami longitudinal ribs, which are somcwhat obscuro behinrl; umboncs promincnt, ancl incurvcd. Lcngth from lhe umbo to thc basal margin two lincs. A single specimcn of this intcresting shcll was clrcdgccl up al Wcymou1h, in August, 1626, adhcring by ils byssus to a largc mass of slate. ORDER II.-DIMYAIIl.A. Shcll providcd wilh two separatc lateral muscular impres- sions. Sun-D1v1s10N I.-LAMELLIPEDEs. FAMILY I-NAYADES. Shells inhabiting frcsh waters ; thc hingc sometimcs with an irregular, simple, or complex tooth, and a lougituclinal prolonged one, ancl sometimes nono. Somc havc a compound muscular impression; ancl thc umbo is frcquently dccorticatccl. GENUS 1.-ANODON.-Brugnicre. Shcll cqui,·alve, inequilatcral, ancl transvcrsc, for the most part very 1hin; hingc linc nearly slraight; hinge glabrous, wi th smooth lamina, dcstitute of cardinal tecth, truncatccl, or form- ing a sinus at the anterior cncl, lcrminating the apcx of thc shcll; Lwo lateral remoto, rnu~cular imprcssions, the posterior onc being compound; pallial imprcssion cntirc, ami seldom clis- tinctly markecl; ligamenl linear, cxtcrnal, sunk in a clefl al the anterior cxtrcmity; inside pearlaceous ; cxlernal surface corcrcd with a shiniug epidermis.