45 



Conch. Icon. Arca, pi. 8. f. 49. , . , t 



Hab. St. Elena, South America (found in sandy mud at the depth 

 of from six to eight fathoms) ; Cuming. 



This shell partakes of the characters of the Arcee Brasiliam and 

 incongrua ; it is however more elongated than either, and the ribs are 

 nairower and more in number. 



Arca. crenata. Arca testd subelongato-quadratd, subcompressd, 

 solidiusculd, vix (equwalvi, lateribus angulato-rotundatis ; albidd, 

 epidermide tenuifuscd indutd; radiatim coutatd, costis septem vel 

 octo et triginta, valvarum ambarum omnibus noduloso-crenatis ; 

 ligamenti ared subangustd, declivi, umbonibus depresso-approxi- 

 matis. 

 Conch. Icon. Arca, pi. 8. f. 51. 



Hab. ? , . ,. . r -u 



This species may be distinguished by its multiplicity of nbs. 

 coupled with the manner in which the whole of them in both valves 

 are crenated. 



Arca globosa. Arca testd globosd, tumidd, subescuivalvi, lateribus^ 

 superne subangulatis, antico breviore ; albidd, epidermide corned 

 fuscd indutd; radiatim costatd, costis duabus vel tribus et triginta. 

 laibus, planulatis ; ligamenti ared mediocri, umbonibus latiusculis, 

 subapproximatis. 

 Conch. Icon. Arca, pi. 8. f. 52. . 



Hab. Catbalonga. island of Samar. Philippines (found in coarse 

 sand and gravel at the depth of four fathoms) ; Cuming. 



Chiefly characterized by its globular form and the smooth horny 

 nature of the epidermis. 



Arca rufescens. Arca testd elongato-ovatd, valde in<equivalvi. la- 

 teribus superne leviter angulatis, infrh rotundatis, postico subelon- 

 gato-extenso ; albidd, rufescente tinctd, epidermide inter costas 

 partim indutd; radiatim costatd, costis numerosis, ąuadragems, 

 confertis, Icevibus ; ligamenti ared mediocri, umbonibus subtrun- 

 catis. 

 Conch. Icon. Arca, pi. 8. f. 53. 



Hab. ? , ^ , . . , • 



This shell is of a more solid structure than the Arca inaguivatvis ; 

 the ribs are much more numerous and close-set, and independent of 

 the difFerence of colour, there is a truncated peculiarity in the um- 

 bones. 



Arca contraria. Arca testd oblique ovatd, solidd, turgidd, cEqui- 

 valvi, lateribus rotundatis, postico brevi, antico elongato-extenso ; 

 albidd, epidermide sericd fuscd crassd partim indutd; radiatim 

 costatd, costis tricenis, lavibus ; ligamenti ared latiusculd, declivi ; 

 umbonibus contrarie contortis. 

 Conch. Icon. Arca, pi. 8. f. 55. 



Hab. ? . ^ , 



This is another contrary or reversed species, and ą very remark- 

 able one, the sheU being completely reversed, whUst the position of 



