126 



the šame peculiar stnicture as those of the Arca ptisilla (Byssoarca 

 pusiUu, Sowerby, Proc. Zool. Soc. 1833) ; the shell is, however, alto- 

 gether larger, more acuminated posteriorly, and the sculpture is of 

 a smaller pattem. 



Arca tenebrica. Arca testu, ohlongo-ovatd , laterihus angulato- 

 rotundatis ; fuscd, epidermide teniii indutd ; rndiatim striatd, striis 

 elevatis, numerosis, confertis ; umbonibus albidis, approrimatis, 

 antice adjectis ; ligamenti ared angustd, postice Janceolato-acumi- 

 natd. 



Conch. Icon. Arca, pi. 16. f. 105. 



Hab. Basey, island of Samar, Philippines (found under stones at 

 low ■tt'ater) ; Cuming. 



The umbones in this species are very anteriorly situated. 



Arca bullata. Arca testd ovato-guadratd, planiusculo-compressd, 

 lateribus superne angulatis, antico infra rotundato, postico angii- 

 lato-extenso ; fuscescente, epidermide tenui, subsetosd, setis in liris 

 longitudinalibus adjectis, indutd ; radiatim costatd, costis nodosis, 

 costis lateralibus grandibus, distantibus, crenato-nodosis ; ligamenti 

 ared angustd, elongatd, declivi. 

 Conch. Icon. Arca, pi. 16. f. 107. 



Hab. ? 



The nodules of the radiating ribs are arranged in longitudinal rows 

 ■svith so much regularity, that the sheU has all the appearance of 

 being cancellated, the effect of which is increased by the bristles of 

 the epidermis being deposited only between the nodules. 



Arca volucris. Arca testd subęuadratd, gibbosd, naviculari, late- 

 ribus superne angulatis, antico infra rotundato, postico angulato, 

 carind acutd ab umbone ad marginėm decurrente ,■ albidd, fusco 

 sparsim iinctd ; striis elevatis longitudinalibus et transversis decus- 

 satd, ared posticali costatd, costis latiusculis, crenatis ; umboiiibus 

 mucronatis, incurvatis ; ligamenti ared latissimd, nigro unimaculatd. 



Conch. Icon. Arca, pi. 16. f. 109. 



Hab. Island of Buriąs, Philippines (found under stones at low 

 •vvater) ; Cuming. 



This species belongs to that division of the genus of Tvhich the 

 Arca No(e is the tj'pe, and is nearest allied to the Arca imbricata. 



Arca ccelata. Arca testd ovato-guadratd, subcompressd, latere 

 antico brevissimo, rotundato, postico angulato, margine ventrali 

 bysso hiante ; albd ; radiatim costatd, costis liris angustis elevatis 

 eleganter clathratis, interstitiis profunde excavatis, costis medianis 

 ditplicatis, lateralibus confertim nodulosis ; umbonibus antice ad- 

 jectis ; ligamenti ared angustd, profunde declivi. 



Conch. Icon. Arca, pi. 16. f. 110. 



Hab. ? 



The sculpture of this shell is of the most exquisite description, 

 and reminds one forcibly of the delicate embossed carA'ing of the 

 Chinese. 



