A \l C A. 



Plate VIII. 



Species 49. (Mus. Cuming.) 



\r\. Area testa subelongato-ovatd, Icnui, valde 

 valvi, lateribus supernl angulato-rotundatis, 

 postico breviore, svbtils angulato-extenso, antico at- 

 tenuate -rotundato ; albidd, rufescente-fusco li/uiii. 

 epidermide tenuissimtt .■ radiatim coslatd, costis ad 

 tr ice n as, anticis iwdttlnsis, posticis minus distinction- 

 bus.planulatis, larvibus, costis valve sinistralis valde 

 latioribus ; ligamenti ared parvd, latiusculd. 



The ovate Ark. Shell rather elongately ovate, thin, 

 very inequivalve, sides angularly rounded at the 

 upper part, posterior side the shorter, angularly ex- 

 tended beneath, anterior side attenuately rounded ; 

 whitish, stained with lighl reddish brown, epider- 

 mis very slight; nidiately ribbed, rihs about thirty 

 in number, anterior nodulous, postei ior less distinet, 

 flat, smooth, ribs of the left valve much broader 

 than those of the right ; area of the ligament small. 

 rather wide. 



Reeve, Pro. Zool. Soc, 1844. 



Hub. St. Elena, South America (found in sandy mud at 

 the depth of from six to eight fathoms) ; Cuming. 



This shell partakes of the characters of theJ/vvr Bra- 

 si/iana and incongrua , it i' however more elongated than 

 either, and the ribs are narrower and more in number. 



Species 50. (Mus. Cuming.) 

 Arca incongrua. Ana testa subquadrato-orbiculari, 



tenuiculii, ra/il'r iiufi/iiiru/ri, lateribus su/ierm 11111/11- 



latis, postico breviore ; albii, epidermide tenui fus- 

 cescente inter costas indutd ,• radiatim costatd, costis 

 septem vel octo et viginti; valvte dextralis anticis 

 gradato-crenatis, sinistralis omnibus crenatis, costis 



valvce sinistralis sub/atioribus ; ared ligamenti latius- 

 cu/ti ; umbonibus subapproximatis. 

 The incongruous Ark. Shell somewhat squarely or- 

 bicular, rather thin, very inequivalve, sides angu- 

 lated at the upper part, posterior side the shorter ; 

 white, covered with a thin light brown epidermis 

 between the ribs ; ribs seven or eight and twenty 

 in number; in the left valve anterior ribs elevately 

 crenated, in the right valve all crenated, ribs of the 

 left valve rather broader than those of the right ; 



arca of the h-.au, rut rather wide; umbones a little 



approximated, 

 Sat, Journ. Acad. Nat. Sci. Philadelphia, vol. ii. 

 Hab. United States. 



The extn posterior ribs of the right, or smaller 

 valve of this shell arc peculiarly narrower than the rest. 



Specie 51. (Mus. Metcalfe.) 

 Arca crenata. Arca testa subelongato-quadratd, sub- 

 i . solidiusiulu, ri.r ,i uiiica/ri, lateribus angu- 

 lato-rotundatis ; albidd, epidermide tenui fused in- 

 dutd; radiatim costatd, costis septem vel octo et tri- 

 gin/a, valvarum ambarum omnibus noduloso-crenatis , 

 ligamenti ared subangustd, declivi, umbonibus de- 

 presso-approximatis. 

 Tim CRl \ vi i n Ark. Shell somew hat elongately square, 

 sed, rather solid, nearly equivalve, 

 - ul.ai ly rounded; whitish, covered with a 

 thin brown epidermis ; radiately ribbed, ribs seven 

 or eight and thirty in number, the whole of which 

 in both valves arc nodulously crenated ; area of the 

 ligamenl rather narrow, bent inwards, umbones 

 depn ssly approximated. 

 Reeve, Pro. Zool. Soc, 1844. 



Hab. ? 



This species may be distinguished by its multiplicity 

 of ribs, coupled with the manner in which the whole of 

 them in both valves are crenated. 



Species 52. (Mus. Cuming.) 

 Arca globosa. Area testa globosd, tumidd, subtequivalvi, 

 lateribus superrie subangulatis, antico breviore ; al- 

 bidd, epidermide corned fused indutd; radiatim cos- 

 tatd , costis daabiis vel tribus et triginta, Icevibus, pla- 

 nulatis , ligamenti ared mediocri, umbonibus /alius- 

 eulis, subapproximatis. 

 The globose Ark. Shell globose, swollen, nearly equi- 

 valve, sides rather angular at the upper part, ante- 

 rior the shorter ; whitish, covered with a brown 

 horny epidermis ; radiately ribbed, ribs two or 

 three and thirty in number, smooth, flat ; area of 

 the ligament middling ; umbones rather broad, a 

 little approximated. 

 Reeve, Pro. Zool. Soc, 1844. 



February 1844. 



