19 



Hab. ad Iquiqui, Peruviae. 



Found attached to stones at lovv water. — G. B. S. 



ByssoARCA TRUNCATA. Byss. testd oblongd, naviculifomn, 

 Jiiscii, parte mcdiand anticuque radiatim sirintis, striis granosis ; 

 carind obtiisd ex umbonead marginėm posticam inferiorem decur- 

 rente ; parte posticd radiatim costatd, costis interstitiisguc ob- 

 tusis, 7-iigosis ; latere anlico brevissimo, supcrne angulato, injrh 

 rotundato, poslico elongato, abrupte truncato ; arcd Ugarnenii 

 elongatd, latd, ligamento qiiadrangulari, prope antkam arece 

 partem soliim adjuncto : long. 2'3, latA'l, alt. 1'2 poli. 



Hab. ad Insulas Gallapagos, saxis adhaerens. 



Tliis species has also been found at Lord Hood's Island attached 

 to Mother-of-pearl Shells. — G. B. S. 



ByssoARCA LURiDA. Bi/ss. tcstd ovato-ohloHgd, decussato-striatd, 

 castaned, epidermidejuscajimbriato-lacerd indutd ; latere antico 

 rotundato, postico obiique truncato ; margine dorsali postice an- 

 gulatd, ventrali postice rotundato-angulatd : long. 1'5, lat.0'75, 

 alt.OSpoU. 



Hab. ad Sanctanv Elenam. 



Found attached to stones, at a depth of twelve fathomsj in rocky 

 ground. 



This species varies in its proportions. — G. B. S. 



ByssoARCA PARVA. Bį/ss. tcsld oblongd, parvd, pulc]ierrim>, de- 

 cussato-striatd, castaned ; latere antico brevi, rotundato, postico 

 elongato ; ared ligamenti breviusculd, angustd : long. O'rf, lat. 

 0'S5, alt. 04i poli. 



Hab. ad littora insularum Oceani Pacifici. 



Found in coral rock, and attached to Motlier-of-psarl Shells, at 

 Ducie's Island. — G. B. S. 



Genus Arca. 

 § iEqulvalves. 



Arca tuberculosa. Arca testd ovali, iurgidd, ohliqud, subauritd, 

 radiatim costatd, costis numerosis, spardm tuberculiferis, antlct 

 prcesertim ; umbonibus proximis ; ared ligamentiferd angustd ; 

 latere antico breviore : long. 28, alt. 2'2, lat. 2-1 poli. 



Hab. ad Real Liejos. 



Found at lovv water at the roots of the Mangrove trees. ' 



Theshell is covered, except the umbones, with a thick dark-bio' n 

 epidermis. — G. B. S. 



Arca Nux. Arca testd ohliqud, turgidd, incBquivalvi, radiatim cos- 

 tatd; valvce dextralis costis anticis graniferis, sinistralis costis oni' 

 nihus graniferis ; umbonibus distantibus, prominentibus ; epider- 

 midejuscd, corned, fenui, ad posticam cost ar um partem setigerd : 

 long. 7, lat. 0-6, alt. 0'65pnll. 



