Zoological Society, 357 



gitudinalihus elevatis fimhriato-decussatd ; ligamenti ared antic^ 

 latiusculd, postice acuminatd ; ligamento brevi, ad posticam area 

 partem solum adjunct o. 

 Conch. Icon. Area, pi. 16. f. 104. 



Hab. Mozambique Channel (found imbedded in madrepore) ; 

 Hankey. 



The ligament and ligamentary area of this species present exactly 

 the same peculiar structure as those of the Area pusilla (Byssoarca 

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

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

 a smaller pattern. 



Arca tenebrica. Area testd oblongo-ovatd, lateribus angulato- 

 rotundatis ; fused, epidermide tenui indutd ; radiatim striatd, striis 

 elevatis, numerosis, eonfertis ; umbonibus albidis, approximatis, 

 antiee adjectis ; ligamenti ared a ngustd, postice lanceolato- acumi- 

 natd. 

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



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

 low water) ; Cuming. 



The umbones in this species are very anteriorly situated. 



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

 lateribus superne angulatis, antico infra rotundato, postico angu- 

 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 

 with so much regularity, that the shell 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 subquadratd, gibbosd, naviculari, late- 

 ribus superne angulatis, antico infra rotundato, postico angulato, 

 carind acutd ab umbone ad marginem decurrente ; albidd, fusco 

 sparsim tinctd ; striis elevatis longitudinalibus et transversis decus- 

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

 mucronatis, incurvatis ; ligamenti ared latissimd, nigro unimaculatd. 

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



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

 water) ; Cuming. 



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

 Arca Noce is the type, and is nearest allied to the Arca imbricata. 



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

 antico brevissimo, rotundato, postico angulato, margine ventrali 

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

 eleganter clathratis, interstitiis profunde excavatis, costis medianis 

 duplicatis, lateralibus confertim nodulosis ; umbonibus antiee ad- 

 jectis ; ligamenti ared angustd, profunde declivi. 



