127 



Akca cometa. Arca testd elongatd, latere antico brevissimo, at' 

 tenuato, rotundato, postico longissimo, plano-angulato ; albidd ; 

 radiatim striatd, striis elevatis, posticis latioribus, prominentibus, 

 dislantioribus, subsquamosis ; umbonibus antice adjectis ; ligamenti 

 ared angustd. 



Conch. Icon. Arca, pi. 16. f. 111. 



Hūb. Sorsogon, island of Luzon, Philippines ; Cuming. 



The posterior strise acąuire almost the importance of ribs. 



Arca oliva,cea. Arca testd ovato-guadratd, tenuiculu, subagui' 

 laterali, lateribus rotvndatis ; albidd, epidermide olivaceo-fuscd 

 teniii corned indutd ; subtilisshne radiatim striatd, striis numerosis, 

 confertis ; ligamenti ared mediocri, umbonibus subcentralibus. 

 Conch. Icon. Arca, pi. 1 G. f. 113. 



Hab. San Nicolas, island of Zebu (found in sandy mud at the deptli 

 of four fathoms) ; Cuming. 



This shell is not much unlike the Arca lactea in general appear- 

 ance ; it will be found, however, on examination to be a much thinner 

 and more delicate shell, ■vvhilst the umbones are sharper and more 

 closely approximated. 



Arca minuta. Arca testd orbiculari-ovatd, subacuivalvi, lateribus 

 superne angulatis, infra rotundatis ; albidd, subpellucidd, epider- 

 mide tenui molli indutd; radiatim striatd ; ligamenti ared latius- 

 culd, ligamento parvo, centrali. 

 Conch. Icon. Arca, pi. 17. f. 112. 



Hab. Philippine Islands (found in coarse sand at the depth of six 

 fathoms) ; Cuming. 



A very minute species, which cannot be referred to any hitherto 

 described. 



Arca navicella. Arca testd ąuadrato- elongatd, subcompressd, 

 lateribus superne angulatis, antico infra rotundato, postico angu- 

 lato, carind ub umbone ad marginėm decurrente ; radiatim striatd; 

 albidd, f usco postice sparsim strigatd ; ligamenti ared elongatd. 



Conch. Icon. Arca, pi. 17. f. 114. 



Hab. Calapan, island of Mindoro, Philippines (found in coarse sand 

 at the depth of ten fathoms) ; Cuming. 



This is a little species of the Arca Nocc or navifonn group. 



Arca lateralis. Arca testd obUqu> trapeziformi, lateribus superne 

 angulatis, antico brevissimo, postico latissitno, obligue expanso ; 

 radiatim costatd, costis numerosis, angiistis, crenatis, epidermide 

 subpilosd indutd; ligamenti ared parvd. 

 Conch. Icon. Arca, pi. 17. f. 115. 

 Hab. Philippine Islands ; Cuming. 



The peculiarly obliąue growth of this species renders it extremely 

 interesting. The posterior side of the shell is radiated w'ith lines of 

 fine dark hair rising from between the crenulations of about everr 

 third rib. 



Arca symmetrica. Arca testd subguadratd, gibbosd, lateribus 



