44 



In this species there is no trace of that peculiar green colour which 

 is so prominent in the foliowing. 



Arca chalcanthum. Arca testd obIongo-quadratd, subcompressd, 

 in<squivalvi, lateribus superne angulatis, latere antico brevissimo, 

 postico latiore, compressd ; albidd, corio corneo viridi, epidermide 

 fuscd, indutd ; radiatim costatd, costis octo et viginti, angustis, 

 valvce sinistralis leviter nodulosis ; ligamenti ared subangustd. 

 Conch. Icon. Arca, pi. 7. f. 43. 



Hab. San Nicolas, island of Zebu, Philippines (found in sandy 

 mud at the depth of six fathoms) ; Cuming. 



The peculiar colour of this shell gives it the appearance of having 

 been stained with green copperas. 



Arca Luzonica. Arca testd elongato-quadrutd, gibbosiusculd, aqui- 

 valvi, lateribus superne angulatis, infra rotundatis , latere antico 

 brevi ; albidd, corio corneo viridescente, epidermide fuscd, indutd; 

 radiatim costatd, costis octo et viginti, latiusculis, valva sinistralis 

 subobsolete nodulosis ; ligamenti ared subangustd, declivi. 



Conch. Icon. Arca, pi. 7. f. 44. 



Hab. Island of Luzon, Philippines (found in sandy mud at low 

 vvater) ; Cuming. 



This is a stouter shell than the preceding species ; it is mere gib- 

 bous, and the ribs are broader. 



Arca rotundicostata. Arca testd cvatd, gibbosd, čequivalvi, la- 

 teribus superne angulatis, antico brevi, rotundato, postico suban- 

 gulato-extenso ; albd, umbones versus fuscescente tinctd ; radiatim 

 costatd, costis ad vicenas, subdistantibus, elevatis, rotundatis, cre- 

 natis, valva sinistralis potius latioribus ; ligamenti ared latd, pau- 

 lulitm concavo-declivi. 



Conch. Icon. Arca, pi. 7. f. 4C. 



Hab. ? 



A species in which the ribs are peculiarly rounded. 



Arca clathrata. Arca testd subguadrato-ovatd, aguivalvi, late- 

 ribus leviter compressis, superne angulatis, infrd. rotundatis; 

 albidd, epidermide tenui fuscescente, inter costas exilissime setosd, 

 indutd; radiatim costatd, costis leviter crenatis, interstitiis pro- 

 fundis, lineis elevatis clathratis ; ligamenti ared subelongatd. 

 Conch. Icon. Arca, pi. 7. f. 48. 



Hab. Islands of Buriąs and Ticao, Philippines (found at the depth 

 of about six fathoms) ; Cuming. 



A small species, in which the interstices betvveen the ribs, which 

 are very deeply engraved, are distinctly latticed with raised lines. 



Arca ovata. Arca testd subelongato-ovatd, tenui, valde inccguivalvi, 

 lateribus superne angulato-rotundatis, postico breviore, subtūs an- 

 gulato-extenso, antico attenuato-rotundato ; albidd, rufescente-fusco 

 tinctd, epidermide tenuissimd ; radiatim costatd, costis ad tricenas, 

 anticis nodulosis, posticis minus distinctioribus, planulatis, leevibus, 

 costis valvee sinistralis valde latioribus; ligamenti ared parvd, 

 latiusculd. 



