ARCA.— Plate XVII. 



The symmetrical Ark. Shell somewhat square, gib- 

 bous, sides sharply angulated at the upper part, 

 anterior rounded beneath, posterior angulated ; 

 greenish ; crenulately decussated with longitudinal 

 and radiating striae ; area of the ligament rather 

 broad, ligament small, central. 



Reeve, Pro. Zool. Soc, 1844. 



Hab. Philippine Islands, bay of Manila ; Singapore (found 

 under stones at low water) ; Cuming. 

 The ligament of this species occupies only a very 



small diamond-shaped space between the umbones. 



Species 118. (Mus. Cuming.) 



Arca scuxr-TiLis. Area tesld oblongo-quadratd, lateribus 

 superne angulatis, infra obtuso-rotundatis ; idbd ; 

 striis longitudinalibus et radiantibus elevatis subtilis- 

 sime clathratd ; ligamenti area latiusculd. 



The finely-carved Ark. Shell oblong-square, sides 

 angulated at the upper part, obtusely rounded be- 

 neath ; white, very finely latticed with raised lon- 

 gitudinal and radiating striae ; area of the ligament 

 rather wide. 



Reeve, Pro. Soc. Zool., 1844. 



Hab. Baclayon, island of Bohol, Philippines (found in 

 sandy mud at the depth of seventeen fathoms) ; 

 Cuming. 

 The engraved sculpture of this shell is of a more 



prominent character than that of the preceding species. 



Species 119. (Mus. Cuming.) 

 Arca parva. Arca testd elongato-oblongd, lateribus ro- 

 tundatis, antico brevissimo, pulcherrime decussato- 

 striatd, striis radiantibus elevatis, confertis, subtilis- 

 sime squamosis; rubido-castaned ; ligamenti area 

 subangustd, antice adjectd. 

 The small Ark. Shell elongately oblong, sides rounded, 

 anterior very short, very beautifully decussately 

 striated, radiating striae raised, close-set, very finely 

 scaled ; reddish chestnut ; area of the ligament ra- 

 ther narrow, situated anteriorly. 

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

 Hab. Ducie's island, Pacific Ocean (found in coral rock, 

 and attached to shells) ; Cuming. 

 A very delicate neatly sculptured shell. 



fuscescente, epidermide molli indutd ; radiatim sub- 

 tUissime striatd ; ligamenti area latiusculd, liga- 

 mento parvo, centrali. 

 The Zebu Ark. Shell somewhat square, gibbous, 

 sides angulated at the upper part, obliquely rounded 

 beneath ; light brown, covered with a soft epider- 

 mis ; very finely radiately striated ; area of the liga- 

 ment rather broad, ligament small, central. 

 Reeve, Pro. Zool. Soc, 1844. 



Hab. Island of Zebu, Philippines (found under stones at 

 low water) ; Cuming. 

 The ligament, as in the Area symmetrica, occupies 

 merely a small diamond-shaped space between the um- 

 bones. 



Species 121. (Mus. Cuming.) 



Arca striata. Area testd subquadrato-oblongd, lateribus 

 obtuse rotundatis ; fuscescente, epidermide molli in- 

 dutd ; radiatim striata, striis elevatis, confertis, pos- 

 ticis distautioribus ; ligamenti ared latiusculd, de~ 

 clivi. 



The striated Ark. Shell somewhat squarely oblong, 

 sides obtusely rounded ; light brown, covered with 

 a soft epidermis ; radiately striated, striae raised, 

 close-set, posterior striae more distant ; area of the 

 ligament rather wide, bent inwards. 



Reeve, Pro. Zool. Soc, 1844. 



Hab. ? 



This shell approaches very nearly to the Arca lactea, 



but it is yet distinct ; the posterior side is longer, it is a 



more compressed shell, and the posterior striae are more 



widely spread. 



Species 120. (Mus. Cuming.) 

 Arca Zebuensis. Arca testd subquadratd, gibbosd, la- 

 teribus superne angulatis, infra oblique rotundatis , 



Species 1 22. (Mus. Cuming.) 

 Arca pulchella. Area testd ovatd, gibbosd, lateribus 

 superne attenuatis, antico brevissimo ; albd ; laminis 

 longitudinalibus prominent ibus , pulcherrime ftmbriatis , 

 ornatd; ligamenti ared antice latiusculd ; umbonibus 

 anticis. 

 The pretty Ark. Shell ovate, gibbous, sides at- 

 tenuated at the upper part, anterior very short ; 

 white; ornamented with very' beautifully fimbriated, 

 prominent, longitudinal laminae ; area of the liga- 

 ment rather wide anteriorly ; umbones anterior. ' 

 Reeve, Pro. Zool. Soc, 1844. 

 Hab. Algeria. 



This species is well distinguished from any yet de- 

 scribed by the very beautifully fimbriated longitudinal 

 laminae. 



