ARC A, 



Species 97. (Mus. Cuming.) 

 Arca vibescens. Arca testd elongatd, lateribus rotun- 



datis, pos/ico leviter angulato, antico subattenuato ; 

 viridescente, epidermide tenui, ad aream posticam se- 

 tosd, indutd'; striis elevatis radiatd ; Ugamenti ared 

 angustissimd, urnbonibus approximatis. 



The verdant Ark. Shell elongated, sides rounded, 

 posterior side slightly angulated ; greenish, covered 

 with a thin epidermis, bristly upon the posterior 

 area ; radiated with elevated striae ; area of the liga- 

 ment very narrow, umbones approximated. 



Reeve, Pro. Zool. Soc, 1*44. 



Hnb. Catbalonga, island of Samar, Philippines (found 

 under stones at low water) ; Cuming. 

 A delicate greenish species, in which the epidermis 



lies on the posterior area in rows of fine bristles. 



Species 98. (Fig. a and b, Mus. Metcalfe.) 

 Arca Britannica. Arca testii oblique trapeziformi, la- 

 teribus superne angulatis, latere antico brevissimo, 

 attcuiiato, postico oblique tingiilitto. infer tie acuminata, 

 carina prominente ab umbone ad marginem decur- 

 rente ; fuscescente ; striis longitudinalibus et trans- 

 versa decussatd ; Ugamenti area latiusculd, urnbo- 

 nibus incurvatis. 

 The British Ark. Shell obliquely trapeziform, sides 

 angulated at the upper part, anterior very short, 

 attenuated, posterior obliquely angulated, acumi- 

 nated at the lower part, with a prominent keel 

 running from the umbone to the acumination ; light 

 brown ; decussated with transverse and longitudi- 

 nal stria? ; area of the ligament rather broad, um- 

 bones curved inwards. 

 Arca tetragona, Auct. Brit. 

 Hab. Britain (coast of Devonshire, &c). 



I introduce this species of Arca with a new name, in 

 order to distinguish it from the Mediterranean Area 

 tetragona, with which it appears to have been con- 

 founded. 



Species 99. (Mus. Cuming.) 

 Arca fasciata. Arca testd oblongd, tenui, compressd, 

 lateribus rotundatis, superne attenuatis; albidd,fas- 



eiis cinereo-purpurasci'iitibus indistinct is concent r in 

 tinctii ; epidermide tenui, postice setosd, indutd ; ru- 

 diatim striatd, striis elevatis, irregularibus, striis 



transrersis sitbti/issimis finibriato-deeussatis ; Uga- 

 menti area angustd, profundi deelici ; intus purpn- 

 raseente. 



The banded Ark. Shell oblong, thin, compressed, 

 sides rounded, attenuated towards the upper part ; 

 whitish, concentrically stained with indistinct bands 

 of ashy purple, covered with a thin epidermis, 

 bristly at the posterior end ; radiately striated, 

 stria* raised, irregular, fimbriately crossed by very 

 fine transverse stria; ; area of the ligament narrow, 

 deeply bent inwards ; interior stained with purple. 



Reeve, Pro. Zool. Soc, 1844. 



Hab. ? 



This is a remarkably flattened shell, banded and 



stained with reddish and ashy purple both inside and 



outside. 



Species 100. (Fig. a and b, Mus. Cuming.) 



Arca tetragona. Area testd elongato-quadratd, late- 

 ribus superne angulatis, latere antico infra rotundato, 

 pos/ico acute ancjulato, eariud acuta ah umbone ad 

 marginem decurrente ; albidd, rubido fuscescenU 

 tinctii ; radialim striatd, striis e/eeatis, subtilissim't 

 crenulatis, rubido-fuscescentibus ; urnbonibus leviter 

 incurvatis ; Ugamenti area lata, rubido-fusco obliqut 

 lineatd. 



The quadrangular Ark. Shell clongately square, 

 sides angulated at the upper part, anterior side 

 rounded beneath, posterior sharply angulated, with 

 a sharp keel running down from the umbone to the 

 margin ; whitish, stained with reddish brown ; ra- 

 diately striated, striae raised, very finely crenulated. 

 reddish brown; unibones slightly incurved ; area of 

 the ligament broad, obliquely lineated with reddish 

 brown. 



Poli, Testacea, vol. ii. pi. 25. f. 12 and 13. 



Hab. Mediterranean. 



The British species, which I have distinguished bv 



the title of Area Britannica, has been hitherto confounded 



with the Area tetragona of the Mediterranean ; it differs. 



however, materially by its peculiarly oblique trapeziform 



growth. 



May 1S44. 



