42 



Conch. Icon. Arca, pi. 5. f. 31. 



Hab. ? 



This is a shell of very peculiar growth, inasmuch as the posterior 

 side is smaller and more attenuated than the anterior, a condition 

 reverse to that usually presented. 



Arca Japonica. Arca testd elongato-ovatd, tenuimld, valde inagui- 

 valvi, lateribiis rotundatis, postico latiore, antico brevissimo ; albd, 

 epldermide cornedfuscescente, inter costas squamosd,indutd ; radi- 

 atim costatd, costis quinqtie et triginta, angustis, Icevibus, planu- 

 latis, ant kis subobsolete nodulosis ; ligamenti ared angustissimd. 



Conch. Icon. Arca, pi. 5. f. 32. 



Hab. Coast of Japan (found in sandy mud) ; Dr. Siebald. 



The lateral extremities of this shell are peculiarly rounded. 



Arca vellicata. Arca testd trapeziformi, subcompressd, in medio 

 leviter contractd, vix ceguivalvi, lateribus superne angulatis, an- 

 tico infrCi rotundato, postico angtilato-expanso ; albidd, epidermide, 

 inter costas sguamosd, partini indutd ; radiatim costatd, costis 

 angustis, mmierosissimis, guinguagenis aut pluribits, anticis sulco 

 divisis ; ligamenti ared angustd ; umbonibus latis, peculiariter de- 

 presso-vellicatis. 



Conch. Icon. Arca, pi. 5. f. 33. 



Hab. : 



' This is a very remarkable shell, both on account of the large 

 number of ribs, and of the peculiar comjjressiou of the umbones. 



Arca Gambiensis. Arca testd elongato-guadratd, tenuiculd, valde 

 compressd, in medio coarctatd, aguivalvi, lateribus rotundatis, 

 postico subangulato extenso ; albidd, epidermide tenui olivaced, 

 sparsim setigerd, indutd ; radiatim costatd, costis duabus vel tribus 

 et viginti, Icevigatis, plano-expansis, lira exili intercurrente ; liga- 

 menti ared parvd, angustd ; umbonibus angulato-mucronatis . 

 Conch. Icon. Arca, pi. 6. f. 3G. 



Hab. Mouth of the Gambia, Africa (found in sandy mud in deep 

 \vater). 



The ribs of this shell become peculiarly liattened and spread out 

 towards the margin, and there is a fine ridge running down the cen- 

 tre of the intermediate grooves. This is the only species in 'vvhich I 

 have as yet observed any kind of fine interribbing. 



Arca cuneata. Arca testd obligue ovatd, ceguivalvi, marginėm 

 versus coarctatd, lateribus superne angulatis, infru obligue rotun- 

 datis ; albidd, radiatim costatd, costis ad vicenas, rotundatis, irre- 

 gulariter nodosis ; ligamenti ared latissitnd, declivi; umbonibus 

 parvis, distantibus. 



Conch. Icon. Arca, pi. 6. f. 37. 



Hab. Zanzibar. 



The great width of the ligamentary area, separating the umbones 

 asunder to a considerable extent, imparts a 'vvedge-like form to this 

 shell, by vvhich it raay be easily recognised. 



