ARCA, 



Plate XI. 



Species 69. (Mus. Cuming.) 



Arca zebra. Area tesld ovato-oblongd, tenuiculd, latere 

 antico brevi, gibbosissimo, tumido, postico elongato, 

 attenuato-compresso, subtruncato, carina prominente, 

 obtusd, ab umbone ad marginem decurrente, margine 

 ventrali hiatu bijssi maxima ; antice alba, postici 

 fused, strigis fuscis undatis undiqui pictd; parte me- 

 diand antiedque radiatim striatis, striis elevatis, no- 

 duloso-crenalis, alternatim majoribus, parte posticd 

 quadricostatd, costis rudibus, obtusis ; umbonibus sub- 

 inclinatis ; ligament i area latissimd, concavd ; sulcis 

 Mgamentariis perpaucis, angustis, in area parte an- 

 ticd ta/itiim incisis. 

 The Zebra Ark. Shell ovately oblong, rather thin, 

 anterior side short, very gibbous, swollen, posterior 

 elongated, attenuately compressed, slightly trun- 

 cated, with a prominent blunt keel running down 

 from the umbone to the margin, ventral margin with 

 a very large opening for the byssus ; anterior side 

 white, posterior brown, painted with brown waved 

 zebra-like streaks ; middle and anterior portions of 

 the shell radiately striated, striae raised, nodulously 

 crenated, alternately larger, posterior four-ribbed, 

 ribs rude, blunt ; umbones bent forwards; area of 

 the ligament very wide, concave ; ligamentary 

 grooves narrow, few in number, engraved on the 

 anterior part of the area only. 



Byssoarca zebra, Swainson, Zoological Illustrations. 

 Hab. Bay of Manila and island of Corregidor, Philippines 

 (found under stones at low water) ; Cuming. 

 The byssus of the Arca zebra is of a dark homy lami- 

 nal structure, and in the specimen here figured is large 

 enough to cover an area upon the substance to which it 

 has adhered, of an oval shape about an inch and a half 

 long by one inch broad. The hinge has a remarkably 

 slight ligamentary connection. 



Species 70. (Mus. Hanley.) 



Arca naviculars. Arca testa quadrato-elongatd, in 

 medio leviter coarctatd, solidiusculd, latere antico ro- 

 tundato, postico compresso-angulato, truncato, mar- 

 gine ventrali bysso vix kiante ; albido-luteold, stri- 

 gis latis perpaucis rubido-brunneis sparsim ornatd ; 

 radiatim costatd, costis prominent ibus, irrcgularibus, 

 stibobsolete tuberculosis ; umbonibus remotis ,■ liga- 

 menti area planulatd, rhombo sulcifero corio corneo 

 nigricantc-fusco induta. 



The ship-like Ark. Shell squarely elongated, slightly 

 contracted in the middle, rather solid, anterior side 

 rounded, posterior compressly angulated, truncated, 

 ventral margin but little gaping ; yellowish white, 

 sparingly ornamented with a very few faint, broad, 

 reddish brown streaks ; radiately ribbed, ribs pro- 

 minent, irregular, rather obsoletely tubercled ; um- 

 bones remote ; area of the ligament flat, the diamond- 



shaped space enclosing the ligamentary grooves 



coated with a dark brown horny cuticle. 

 Bruguiere, Enc. Meth.vers, p. 99. 



Arca Noa, var., Chemnitz, Conch. Cab., vol. vii. 

 pi. 54. f. 533. 



Arca retusa ? Lamarck. 

 Hab. China (attached to stones). 



Neither Lamarck nor Deshayes appears to have been 

 acquainted with this interesting and rare species, though 

 accurately described by Bruguiere, and as accurately 

 figured by Chemnitz. It is not the Mediterranean Arca 

 tetragona of Poli, as those authors supposed, but one 

 of distinct character, from a very remote locality. 



Species 71. (Mus. Cuming.) 

 Arca maculata. Arca testa oblique oblongd, subrhom- 

 boided, gibbosissimo,, lateribus superne angulatis, an- 

 tico parvo, postico vald'e longiore, carind validd ab 

 umbone ad marginem decurrente, margine ventrali 

 bysso paululitm kiante ; albidd, postici fusco pallide 

 maculata ; superficie tutti laminis Jimbriatis, gradatim 

 digestis, siibti/issimi- inscu/ptd ; ligament i ared latius- 

 cu/ii, rhombo sulcifero parvo, antic':: disposito. 

 The spotted Ark. Shell obliquely oblong, somewhat 

 diamond-shaped, very gibbous, sides angulated at 

 the upper part, anterior small, posterior much 

 longer, with a strong keel running down from the 

 umbone to the margin, ventral margin but little 

 gaping; whitish, palely spotted on the posterior 

 side within the keel with brown ; entire surface very 

 finely carved with fimbriated lamina?, arranged one 

 over the other like steps ; area of the ligament 

 rather wide, the diamond-shaped space enclosing 

 the ligamentary grooves small, situated anteriorly. 

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

 Hab. Lord Hood's Island, Pacific Ocean (found attached 

 to large shells) ; Cuming. 



The Arca maculata, as Mr. Sowerby notices, is co- 

 vered with a thin pale-coloured epidermis, which is very 

 conspicuous on the posterior ridge, where it forms a row 

 of plumose bristles. 



Species 72. (Mus. Cuming.) 

 Arca No.e. Arca testa elongato-oblongd, latere antico 

 brevissimo, subattenuuto-coarctato, postico subcom- 

 presso-expanso, superne emarginato, carina obtusd 

 ab umbone ad marginem decurrente, margine ventrali 

 bysso plus minusve kiante; fused, mediant incarnato- 

 albd, fusco undatim strigatd ; radiatim costatd, costis 

 rudibus, irregidaribus, sijuamoso-rugosis, antico-me- 

 dianis fere obsoletis ; ligamenti area plano-eoncavd. 

 Noah's Ark. Shell elongately oblong, anterior side 

 very short, somewhat attenuately contracted, pos- 

 terior rather compressly expanded, emarginated to- 



