ARCA.— Plate XIV. 



umbones rather approximated, situated anteriorly ; 



area of the ligament narrow, bent inwards. 

 Linnaeus, Mus. Tessinianum, p. 116. pi. 16. f. 1. 

 Hab. Island of Mindoro, Philippines (found under stones 



at low water) ; Cuming. 



This shell may be known by the radiating rows of 

 scales and bristles of the epidermis, which are remark- 

 ably strongly developed on the posterior side. The 

 teeth in this species are not set in a straight line, but 

 describe a curve indicating an approach to the hinge of 

 Pectunculus. 



Species 94. (Mus. Cuming.) 



A rca setigera. Arca testd subquadrato-oblongd, late- 

 ribus rotundatis, postico latiore, margine ventrali 

 bysso vix hiante ; rubido-fascd, epidermide fused seti- 

 gera indutd ; radiatim subtilissimi striata, s/riis ele- 

 vatis, granulosis; umbonibi/s suhupprojrimatis, antice 

 adjectis ; ligament! area angustd, declivi. 



The bristly Ark. Shell rather squarely oblong, sides 

 rounded, posterior wider, ventral margin gaping 

 for the passage of the byssus ; reddish brown, co- 

 vered with a brown bristly epidermis ; very finely 

 radiately striated, striae raised, granulous ; umbones 

 rather approximated, situated anteriorly ; area of 

 the ligament narrow, bent inwards. 



Reeve, Pro. Zool. Soc, 1844. 



Hab. Zanzibar (found under stones at low water) ; I 

 Thorn. 



This species approaches very closely to the preceding ; ! 



it appears, however, to be of an uniform smaller size, the ' 



posterior side is less expanded, and the bristles are set ] 

 in single rows. 



Species 95. (Mus. Cuming.) 

 Arca lurida. Area testd oblique oblongd, latere antico 

 atte/iuato-rotundato, postico oblique truncato. margine 

 ventrali bysso hiante ; fused, rufeseente tinetd, epider- 

 mide fused, sparsim setosd, indutd ; radiatim striatd, 

 striis granulosis ; umbonibus subapproximatis ; liga- 

 menti area angustd. 



The lurid Ark. Shell obliquely oblong, anterior side 

 attenuately rounded, posterior obliquely truncated, 

 ventral margin gaping for the passage of the byssus ; 

 brown, stained with light red, covered with a 

 brown sparingly bristled epidermis ; radiately 

 striated, stria; granulous ; umbones somewhat ap- 

 proximated ; area of the ligament narrow. 

 Byssoarca lurida, Sowerby, Pro. Zool. Soc, 1833. 



Hab. St. Elena, West Columbia (found attached to 

 stones in rocky ground at the depth of twelve fa- 

 thoms) ; Cuming. 



The Area lurida may be distinguished from the Arca 

 setigera by its more oblique form, whilst it is of a more 

 reddish stained brown colour and has fewer radiating 

 rows of bristles. 



Species 96. (Mus. Cuming.) 



Arca nivea. Arca testd subquadrato-oblongd, gibbosd, 

 lateribus superrie attenuatis, antico rotundato, postico 

 obtuso-angulato, margine ventrali bysso hiante ; nived, 

 radiatim striatd, striis elevatis, prominentibus, epi- 

 dermide crassd squamosd versus marginem indutd ; 

 umbonibus majuscutis, anticis ; ligamenti ared latius- 

 culd, profundi declivi. 



The snow-white Ark. Shell somewhat squarely ob- 

 long, gibbous, side attenuated towards the upper 

 part, anterior rounded, posterior obtusely angulated, 

 ventral margin gaping for the passage of the bys- 

 sus ; snow-white, radiately striated, stria; raised, 

 prominent, covered towards the margin with a thick 

 scaly epidermis ; umbones rather large, anterior ; 

 area of the ligament rather broad, deeply bent in- 

 wards. 



Chemnitz, Conch. Cab., vol. vii. pi. 54. f. 538. 

 Arca ovata, Gmelin, Lamarck. 



Hab. Zanzibar. 



This is not a local variety of the Arca Helblingii, as 

 M. Deshayes has been inclined to suppose; the um- 

 bones in that species are much more central and the 

 valves more flatly compressed. 



