Zuolugical Society. 359 



interesting. The posterior side of the shell is radiated with lines of 

 fine dark luiir rising from lietwcen the crenulations of about every 

 third rib. 



AacA SYMMETRICA. Arca testa subquadratd, gibbosd, lateribus 

 superne acute anguhitis, antico infra rotundato, poslico angulaio ; 

 viridescente ; siriis loiiyitudinulibus et rudiuntibus ercnulato-decvs' 

 satd ; ligumenti area lutiuseuld, ligamento purvo, centrali. 

 Conch. Icon. Arca, pi. 17. f. 117. 



Hab. Philipjiine Islands, bay of Manila ; Singapore (found under 

 stones at low water) ; Cuming. 



Tlie ligament of this species occupies only a very small diamond- 

 shaped space between the umbones. 



Arca sculptilis. Arca testd oblong o- quadrat d , lateribus superne 

 anguhitis, infra obtuso-rotundatis ; ulbd ; striis longitudinalibus et 

 radiantibus elevutis subtilissiinf clathratd ; ligameuti ared latius- 

 cuhl. 

 Conch. Icon. Arca, pi. 17. f. 118. 



Ilab. Baclayon, island of Bohol, Philippines (found in sandy mud 

 at the depth of seventeen fathom?) ; Cuming. 



The engraved sculpture of this shell is of a more prominent ciia- 

 racter than that of the preceding species. 



Arca zebuensis. Arca testd subquadratd, gibbosd, lateribus su- 

 perne anguhitis, infra oblique rotundatis ; fuscescente, epidermide 

 molli indutd ; radiatim subtilissime striatd ; ligamenti ared latius- 

 culd, ligamento parvo, centrali. 

 Conch. Icon. Arca, pi. 17. f. 120. 



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

 water) ; Cuming. 



The ligament, as in the Arca symmetrica, occupies merely a small 

 diamond-shaped space between the umbones. 



Arca striata. Area testd subquadrato-oblongd , lateribus obtuse 

 rotundatis ; fuscescente, epidermide molli indutd ; radiatim striatd, 

 striis elevatis, confertis, post ids distantioribus ; ligamenti ared 

 latiusculd, declivi. 

 Conch. Icon. Arca, pi. 17. f. 121. 



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. 



Arca pulchella. Arca testd ovatd, gibbosd, lateribus superne 

 attcnuatis, antico brevissimo ; albd ; laminis longitudinalibus pro- 

 minent ibus, pulcherrime fimbriatis, ornatd ; ligamenti ared antici 

 latiusculd ; umbonibus anticis. 



Conch. Icon. Arca, pi. 17. f. 122. 



Hab. Algeria. 



This species is well distinguished from any yet described by the 

 very beautifully fimbriated longitudinal laminoe. 



