Zoological Society. 489 



The ribs of this shell are very finely pricked or indented, a charac- 

 ter which I do not remember to have observed in any other species. 



Arca cistula. Area testd subquadratd, incequivalvi, lateribus su- 

 perne angulatis, antico infra rotundato, postico quadrato ; albd, 

 epidermide tenui fuscescente , inter costas squamosa, indutd; radi- 

 atim costatd, costis angustis, numerosis, septemvelocto et triginta, 

 valval sinistralis umbones versus subtilissime nodulosis ; Ugamenti 

 ared mediocri; umbonibus subacutis, prope extremitatem anticam 

 dispositis. 



Conch. Icon. Arca, pi. 5. f. 29. 



Hab. ? 



An interesting species, remarkable for the neatness and regularity 

 of the ribs, as well as for the very anterior situation of the umbones. 



Arca inflata. Arca testd oblique ovatd, tenui, inflatd, vix cequi- 

 valvi, lateribus superne leviter angulatis, infra rotundatis ; albidd, 

 epidermide corned fused, inter costas squamosd, indutd ; radiatim 

 costatd, costis numerosis, quadragenis, planulatis, Icevibus ; Uga- 

 menti ared subangustd, declivi ; umbonibus tumidis, paululum ap- 

 proximatis. 



Conch. Icon. Arca, pi. 5. f. 30. 



Hab. Ilo Ilo, isle of Panay, Philippines (found in soft mud at the 

 depth of six fathoms) ; Cuming 



This is a light inflated shell of rather large size, at present unique 

 in the collection of Mr. Cuming. 



Arca cymb^eformis. Arca testd elongato-ovatd, tumidiusculd, in- 

 cequivalvi, postice attenuatd ; albidd, epidermide corned viridescente, 

 inter costas squamosd, indutd ; radiatim costatd, costis duabus et 

 triginta, valva sinistralis rotundatis, tuberculato-crenatis, valval 

 dextralis planulatis, anticis tantum crenatis ; Ugamenti ared parvd, 

 declivi. 



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. Area testd elongato-ovatd, tenuiculd, valde inaqui- 

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

 epidermide corned fuscescente, inter costas squamosd, indutd ; radi- 

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

 latis, anticis subobsolete nodulosis ; Ugamenti 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 cequivalvi, lateribus superne angulatis, an- 

 tico infrh rotundato, postico angulato-expanso ; albidd, epidermide, 

 inter costas squamosd, partim indutd; radiatim costatd, costis 

 angustis, numerosissimis, quinquagenis aut pluribus, anticis sulco 



