AHCA. 



X. 



Hab. San Miguel, South America (found in sandy mud) ; 

 Cuming. 

 This is a fine bold species, but it does not exhibit any 

 very striking peculiarity of character. 



Species 67. (Mus. Cuming.) 

 Arca labiosa. Area testa oblique ovatd, compressii, in- 

 (Equivalvi, lateribus superne angulatis, antico infrd, 

 rotundato, postico obtuso-angulato ; albd, epidermide 

 corned fuscescente indutd; radiatim costata, costis 

 numerosis, septem vel octo et triginta, anticis obsolete 

 rugulosis, costis valvce sinistralis sublatioribus ; li- 

 gamenti ared angustissimd. 

 The full-lipped Ark. Shell obliquely ovate, com- 

 pressed, inequivalve, sides angulated at the upper 

 part, the anterior rounded beneath, the posterior 

 obtusely angled ; white, covered with a light brown 

 epidermis ; radiately ribbed, ribs numerous, seven 

 or eight and thirty in number, the anterior ribs ob- 

 soletely wrinkled, ribs of the left valve rather wider 

 than those of the right ; area of the ligament very 

 narrow. 

 Sowerby, Pro. Zool. Soc, 1833. 



Hab. Tumbez, coast of Peru (found in soft mud at the 

 depth of seven fathoms) ; Cuming. 

 The circumstance of this shell having been known to 

 Mr. Sowerby only in a very young state will account 

 for the apparent discordance of our descriptions. 



Species 68. (Mus. Hankey.) 



Arca Hankeyana. Arca testd oblique ovatd, crassius- 

 Cli/ei, valdi cjibbosii, tumidii, « ijtiiralvi, lateribus ro- 

 tundatis, superne attenuatis, latere antico brevissimo, 

 postico oblique extenso ; albd, epidermide tenui, inter 

 castas hirsutd, sparsim indutd; radiatim costata, 

 costis duabus vel tribus et triginta, planulatis, con- 

 fertis, quadriliratis ; umbonibus parvis, distantibus ; 

 lirjamenti ared brevi, lata, declivi. 

 Hankey's Ark. Shell obliquely ovate, rather thick. 

 very gibbous, swollen, equivalve, sides rounded, at- 

 tenuated at the upper part, anterior side very short, 

 posterior obliquely extended ; white, sparingly co- 

 vered with a slight epidermis that is hairy between 

 the ribs ; radiately ribbed, ribs two or three and 

 thirty in number, flat, close-set, composed of four 

 ridges ; umbones small, distant ; area of the liga- 

 ment short, wide, and bent inwards. 

 Reeve, Pro. Zool. Soc, 1844. 



Hab. Harbour of Mozambique (found in a mass of white 

 coral on the reefs at low water, spring tide) ; Han- 

 key. 

 I close this division of the genus with the new species, 

 which exhibits a peculiarity in the structure of the ribs 

 of great novelty and interest, each of them being com- 

 posed of four distinctly separated ridges. 



And I have great pleasure in naming this important 

 species after the gentleman to whom I am indebted for 

 it, Lieut. Hankey, R.N., a zealous conchologist, whose 

 researches on the coast of Africa have greatly contri- 

 buted to science. 



