20 



Hab. ad Xiplx<npi. 



Found in sandy mud at a depth of twelve fathoms. — G. B, S. 



Arca reversą. Arca testd obliąud, turgidd, radiatim costatd, 

 costis riigulosis ; latere postico longiore, rotundato, antico bre- 

 viore, obligufi truncato ; umbonibus approximatis ; ared iiąarnen- 

 tiferd angnstd, omnino posticd ; epidermidej'uscd, crassd, hirsutd : 

 long. ]-15, lat.O-S, alt. 09 poli 



Hab. in PeruviA. 



Found in soft mud, at a depth of seven fathoms, at Tumbez. 



Named by Mr. Gray from a specimen in Mr. Fov's cabinet. — 

 G. B. S. 



Arca concinna. Arca testd oblongd, incEqitivnlvi,alld, radiatim 

 costatd, costis anticis rugulosis, interstitiis decussatis ; latere an- 

 tico breviore, svpertiė angulato ; latere postico pone angulum 

 inconspicuum productiore ; ared ligamenti angustd, antice utrin. 

 que crenidatd ; ligamento postico ; epidermidc olivaced, ad sukos 

 antice postictcue spiniferd : long. 1-1,5, lut. 5, alt. 0-65 poli. 



Hiib. in America Centrali. 



Found in coarse sand, at a depth of tvvelve fathoms, in the Gulf 

 ofNocoiyo.— G. B. S. 



Arca emarginata. jirca testd oblongd, subctjlindraced, inaąui- 

 valvi, albd, radialini costatd; latere antico brcv'i, costis angris. 

 tioribus, rugulosis ; latere postico elongato, costis latioribus, Ice- 

 vihus ; margine posticd superiore emarginata ; ared ligamenti 

 angustd; epidermidej'uscd, ud sukos sctosd : kng. 1-6, lat.Ol, 

 alt. O H poli. 



Hab. ad Httora Maris Pacifici. 



From Atacamas, Real Liejos, Xipixapi, Panama, and the Gulf of 

 California. — G. B. S. 



Ahca formosa. ^rca testd oblongd, subcylindricd, albicante, ra- 

 diatim costatd, epidermide ftiscd squamoso- sctosd ohtectd ; costis 

 numerosis, pl<mtdalis,anterioribus duplicatis ; margine cardinali 

 utrdęue angulatd; latere antico breviore; ared cardiyiali elongatd , 

 latiusculd : lo7ig. 4:-8, lat. 2-3, alt. ^2-'3 poli. 

 Hab. in America Centrali. (Gulf of Tehuantepec.) 

 This very fine species of Arca niost nearly resembles the Arca 

 Scapha, but is much longer in proportion to its breadth and height. 

 lt is covered, in the interstices of the ribs, with long, pointed scales, 

 vvhich become longer bristly hairs at the posterior side. — G. B. S. 



Arca auriculata. Arca testd oblongd, albd, radiatim costatd, 

 epidermide fuscd sguamoso-setosd obtectd ; margine cardinali 

 utrdųue, prcecipui postice, auriculata : long. I -2, lat. 0*6, alt. 0*65 

 poli. 



Haij. ad Sanctam Elenam. 



Found, at a depth of ten fathoms, in a muddy bottom. — G. B. S. 



