41 



divided by a narrow cut ratlier than a groove ; the scattered brown 

 spots, though few in number, are also peculiar to the Arca maculosa. 



Arca compacta. Arca testii suhelongato-quadratd, inaquivalvi, 

 gibbosd, lateribus superne angulatis, antico breviore, postico leviter 

 angulato-extenso ; albidd, epidermidefuscdpartim indutd ; radiatim 

 costatd, costis tricenis, valvcB dextralis subangustis , planulatis, 

 sinistralis latioribus, rotundatis, interstitiis cancellatis ; ligamenti 

 ared subangustd, declivi. 



Conch. Icon. Arca, pi. 5. f. 27. 



Hab. .? 



This is a short compact shell of rather solid growth. 



Arca pertusa. Arca testd subobligue guadratd, vix esįuivalvi, 

 lateribus snperne angulatis, infrd rotundatis ; albidd, viridescente 

 tinctd, epidermide fuscd spursim indutd ; radiatim costatd, costis 

 duabus vel tribus et triginta, confertis, plano-convexis, subtiUssime 

 pertusis ; ligamenti ared latiusculd, umbonibus subcentralibus. 



Conch. Icon. Arca, pi. 5. f. 28. 



Hab. Mouth of the Gambia, Africa. 



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. Arca testd svbguadratd, inceguivalvi, lateribus su- 

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

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

 atim costatd, costis angustis, numerosis, septem vel octo et triginta, 

 valvce sinistralis umbones versus subtiUssime nodulosis ; ligamenti 

 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 verj' anterior situation of the urabon&s. 



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

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

 epidermide corned fuscd, inter costas sguamosd, indutd ; radiatim 

 costatd, costis numerosis, guadragenis, planulatis, hevibus ; liga- 

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

 proximatis. 



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



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

 depth of six fathoms) ; Cuming. 



This is a light inflated shell of rather ląrge size, at present UDique 

 in the coUection of Mr. Cuming. 



Arca cymb.«:formis. Arca testd elongato-ovatd, tumidiusculd, in~ 

 <Bqulvalvi, postice attenuatd ; albidd, epidermide corned viridescente, 

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

 triginta, valvee siHL<itralis rotundatis, tuberculato-crenatis, valv/e 

 deitralis planulatis, anticis tantum crenatis ; ligamenti ared parvd, 

 declivi. 



