43 



ArCa secticostata. Arca tesld elongato-ovatd, yibbosiss'und, lenui- 

 aild, lateribus superne unyulatis, infru suboblique rohmdatis ; ul- 

 bidd, fuscescente partim tinctd ; radiatim costatd, costis numerosis, 

 angustis, ad gitadragems, guamplurimis sulco subprofundo divisis ; 

 ligamenti ared olongatd, latuisculd ; nmbonibus tumidis. 



Conch. Icon. Arca, pi. 6. f. 38. 



Hab. ? 



This shell is probably one of those that have been confounded 

 with the Arca antiąuata ; it diifers in having a much greater number 

 of ribs, and a larger proportion of them more distinctly grooved. 



Arca ferruginea. Arca testd ovato-oblongd, ceąuivalvi, lateribus 

 rotundatis; albidd, epidermide ferrugineo-fuscd iiidutd; radiatim 

 costatd, costis ad septem et viginti, angustis, compressis, subtilis- 

 sime nodulosis; ligamenti ared subangustd; umbonibus obligui iii- 

 curvis. 



Conch. Icon. Ai'ca, pi. 6. f. 39. 



Hab. ? . ^ , 



The ribs of this species are unusually naiTow, and being finely 

 nodulous, present a kind of beaded appearance. 



Arca radiata. Arca testd ovato-oblongd, tsįuivalvi, lateribus ro- 

 tundatis; albidd, fuscescente ad umbones tinctd, epidermide spur- 

 sim indutd; radiatim costatd, costis ad tricenas, nngustissimis, 

 obsoletb nodulosis. interstitiis clathratis ; ligamenti ared mediocri. 

 Conch. Icon. Arca, pi. 6. f. 40. 



Hab. ? . ^ 



The ribs are much less prominently developed than in the prece- 

 ding species; they are also narrower, more numerous, and less 

 strongly noduled. 



Arca oblioua. Arca testd ovatd, valde obliųud, rcguivalvi, lateri- 

 bus superne angulatis, infrh rotundatis, antico brevissimo, postico 

 obligue expanso ; albd, epidermide fuscescente sericd, inter costas 

 setosd, indutd; radiatim costatd, costis quinque vel sex et triginta, 

 planulutis, confertis, interstitiis subtilissimė striatis, anticis pos- 

 ticisgue leviter crenatis, anticis sulco divisis; ligamenti ared sub- 

 angustd, declivi ; umbonibus approximatis. 



Conch. Icon. Arca, pi. 6. f. 41. 



Hab. West coast of Africa. 



This is a very interesting species, and altogether one of very di- 

 stinct character. 



Arca myristica. Arca testd subguadrato-ovatd, gibbosiusculd ,^ 

 inccguivalvi, lateribus angulato-rotundatis ; albd, epidermide temti 

 rubido-fuscescente indutd; radiatim costatd, costis tribusvel gva- 

 tuor et viginti, valva sinistralis omnibus nodulosis, dextrans anticis 

 tantum ; ligamenti ared subangustd. 



Conch. Icon. Arca, pi. 7. f. 42. / . , • 



Hab. Jimamailan, island of Negros. Philippines (tound m saudy 

 mud at the dcpth of three fatlioms) ; Cumirig. 



