ARCA.— Plate XVI. 



naliter fimbriato-costatd, interstitiis prof uncle sulcatis, 

 liris elevatis august is decussatis ; costis carinam super 

 fimbriato-spinosis, ad aream posticam concavam diva- 

 Heat im radiatis ; ligamenti area angustd, postice 

 lanceolate!. 

 The divaricated Auk. Shell ovately oblong, anterior 

 side rather angulated at the upper part, posterior 

 rounded, somewhat concavely compressed, with a 

 keel running down from the umbone to the margin ; 

 white, with scarcely any epidermis ; longitudinally 

 rimbriately ribbed, interstices deeply grooved, 

 crossed with narrow raised ridges ; ribs fimbriately 

 spinous on passing over the keel, divaricately rayed 

 across the concave posterior area ; area of the liga- 

 ment narrow, lanceolated posteriorly. 

 Byssoarca divaricata, Sowerby. 

 Hah. Island of Annaa (Chain Island), Pacific Ocean 

 (found attached to stones) ; Cuming. 

 This very pretty species is most characteristically di- 

 stinguished by the divaricated course of the ribs over the 

 posterior area. 



Species 109. (Mus. Cuming.) 



Arca volucris. Area testd subquadratd, gibbosd, navi- 

 cular!, lateribus superne angulatis, antico infra ro- 

 tundato, postico angulalo, carind acuta ab umbone ad 

 marginem decurrente ; albidd, fusco sparsim tinctd ; 

 striis elevatis longitudinalibus et transversis decus- 

 satd, ared posticali costatd, costis latiusculis, cre- 

 natis; umbonibus mucronatis, incurvatis; ligamenti 

 ared latissimd, nigra unimaeu/atd. 



The flying-bird Ark. Shell somewhat square, gib- 

 bous, boat-shaped, sides angulated at the upper 

 part, anterior rounded beneath, posterior angulated, 

 with a sharp keel running down from the umbone 

 to the margin ; whitish, sparingly tinged with 

 brown ; decussated with transverse and longitudi- 

 nal raised stria? ; posterior area ribbed, ribs rather 

 broad, crenated ; umboues pointed, curved inwards ; 

 area of the ligament very broad, marked with a 

 dark blotch. 



Reeve, Pro. Zool. Soc, 1844. 



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 Noee is the type, and is nearest allied to 

 the Area imbricata. 



Species 110. (Mus. Cuming.) 

 Arca ccelata. Arca testd ovato-quadratd, subcompressd, 

 latere antico brevissimo, rotundato, postico angulato, 

 margine ventrali bgsso hiante ; albii ; radial im ens- 

 lata, cos/is /iris angustis elevatis elegant, r clathratis, 

 interstitiis profundi excavatis, costis mediants dupli- 

 eatis, lateralibus confertim nodulosis ,■ umbonibus 

 antice adject is ; ligamenti an a angustd, profundi de- 

 clivi. 



The embossed Ark. Shell ovately quadrate, rather 

 compressed, anterior side very short, rounded, pos- 

 terior angulated, ventral margin gaping for the 

 passage of the byssus ; white ; radiately ribbed, 

 ribs elegantly latticed with narrow raised ridges, 

 interstices deeply excavated, middle ribs duplicate, 

 side ribs closely noduled ; umbones situated ante- 

 riorly ; area of the ligament narrow, bent inwards. 



Reeve, Pro. Zool. Soc, 1844. 



Hab ? 



The sculpture of this shell is of the most exquisite 

 description, and reminds one forcibly of the delicate em- 

 bossed carving of the Chinese. 



Species 111. (Mus. Cu 



Arca cometa. Arca testd elongatd, latere antico bre- 

 vissimo, attenuate rotundato, postico longissimo, 

 plano-angulato ; albidd ; radiatim striata, striis ele- 

 vatis, postieis latioribus, prominentibus, distantioribus, 

 subsquamosis ; umbonibus antice adjectis ; ligamenti 

 area angustd. 



The comet Ark. Shell elongated, anterior side very 

 short, attenuated, rounded, posterior very long, 

 flatly angulated ; whitish ; radiately striated, striae 

 raised, posterior stria? wider, prominent, more di- 

 stant, a little scaly ; umbones situated anteriorly ; 

 area of the ligament narrow. 



Reeve, Pro. Zool. Soc, 1844. 



Hab. Sorsogon, island of Luzon, Philippines; Cuming. 



The posterior stria? acquire almost the importance 

 of ribs. 



For Species 112 (Area pusilla), see Plate XVIII., the 

 shell here figured being merely a somewhat distorted 

 specimen of the Arca divaricata. 



Species 113. (Mus. Cuming.) 



Arca olivacea. Arca testa ovato-quadratd, tenuiculd, 

 subaquilaterali, lateribus rotundatis ; albidd, epider- 

 mide nlieaeeo -fused tenui earned indutii ; subtilissime 

 radiatim striata, striis numerosis, cunfertis ; liga- 

 menti area mediocri, umbonibus subcentralibus. 

 The olive-coloured Ark. Shell ovately square, rather 

 thin, nearly equilateral, sides rounded; whitish. 

 covered with a thin, horny, olive-brown epidermis; 

 very finely radiately striated, stria numerous, close- 

 set ; area of the ligament middling, umbones 

 nearly central. 

 Reeve, Pro. Zool. Soc, 1844. 



Hab. San Nicolas, island of Zebu (found in sandy mud 

 at the depth of four fathoms) ; Cuming. 

 This shell is not much unlike the Arca luetea in ge- 

 neral appearance ; it will be found, however, on exami- 

 nation to be a much thinner and more delicate shell, 

 whilst the umbones are sharper and more closely ap- 

 proximated, 



