Zoological Society. 491 



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

 sim itidufd ; radiathn costatd, costis ad tricenas, angustissimis, 

 obsolete nodulosis, interstitiis cluthratis ; ligamenti ared 7nediocri, 

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



Hab. ? 



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

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

 strongly noduled. 



Arca obliqua. Area testa ovatd, valde obliqud, cequivalvi, lateri- 

 bus superne nngulatis, infrd. rotundatis, antieo brevissimo, postico 

 oblique expanse ; albd, epidermide fuscescente sericd, inter castas 

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

 plamdatis, confertis, interstitiis subtilissime striatis, anticis pos- 

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

 angustd, declivi ; umbonibus upproximatis. 

 Conch. Icon. Area, 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 testa subqiiadrato-ovatd, gibbosiusculd, 

 incEquivalvi, lateribus angulato-rotundntis ; albd, epidermide tenui 

 riibido-fuscescente indutd ; radiatim costatd, costis tribus vel qua- 

 tuor et viginti, valvcB sinistralis omnibus nodulosis, dextralis anticis 

 tantum ; ligamenti ared subangustd. 

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



Hab. Jimamailan, island of Negros, Philippines (found in sandy 

 mud at the depth of three fathoms) ; Cuming. 



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

 is so prominent in the following. 



Arca chalcanthum. Arca testa oblongo-quadratd, subcompressd, 

 incequivalvi, lateribus superne angulatis, latere antieo brevissimo, 

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

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

 valva 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 testa elongato-quadrutd, gibbosiusculd, cequi- 

 valvi, lateribus superne angulatis, infra rotundatis, latere antieo 

 brevi ; albidd, corio corneo viridescente, epidermide fused, 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 

 water) ; Cuming. 



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

 bous, and the ribs are broader. 



