34 THE VOYAGE OF H.M.S. CHALLENGER. 



eight) inequidistant radiating ridges, wliicli do not, however, extend quite up to the beaks. 

 These in both valves are smooth, rather glossy, almost snow-white, and well rolled in 

 and forward. The right valve has a simple strong erect cardinal tooth immediately beneath 

 the beak, which fits into a corresponding pit in the left valve, behind which is a stout 

 process or denticle supporting the ligament. The interior is more or less stained with 

 brown, the anterior scar elongate, the posterior rounder, and the pallial line faintly sinuated. 



Length 6 mm., height 5 J, diameter 3f. 



Habitat. — Station 33, off Bermuda, in 435 fathoms ; coral mud ; (Challenger) ; 

 Hayti (Coll. Cuming in British Museum). 



This interesting little species does not appear to agree with any of the numerous 

 forms already described from the West Indian region. In the inequality of the valves it 

 resembles Corbula ojyerculata, Philippi, from St. Thomas Island, but differs from that 

 species in size, form, the absence of the double keel in the right valve, and in the difiierent 

 sculpture of the left. 



Corbula monilis, Hinds. 



Corbula monilis, Hinds, Proc. Zool. Soc. Lond., 1843, p. 58. 

 uorhula monilis, Eeeve, Conch. Icon., vol. ii. pi. v. fig. 35. 



Testa minuta, alba, globosa, paulo inaequdateralis, antice rotundata, postice leviter 

 producta, plus minusve truncata. Margo dorsi utrinque valde declivis, leviter arcuatus, 

 ventralis late curvatus, postice paululum sinuatus. Valvse mediocriter tenues, valde 

 insequales, liris concentricis gracilibus instructse. Umbones magni, inflati, prominentes, 

 antrorsum curvati. 



This species, several specimens of which were obtained, all of the same minute 

 dimensions, is somewhat inequilateral, considerably inflated, moderately thick for so smaU 

 a shell, white, inequivalve, and marked with fine concentric lirse. . The dorsal slopes are 

 somewhat curved and very oblique, the ventral outline being slightly arcuate, and a little 

 sinuated posteriorly. The anterior end is sharply rounded, the hinder extremity being 

 a. little produced and somewhat truncated. The umbones are rather large, elevated 

 above the hinge line, and terminate in a minute glossy tip curved over towards the 

 front. The right valve has a single erect, strong tooth, immediately beneath the apex 

 of the beak, and in the left there is a triangular pit for its reception. 



Length 2 mm., height If, diameter 1^. 



Habitat. — Stations 186, 187, and 188, all in Torres Strait, North Australia, in 3 to 

 28 fathoms. 



This minute form was originally described from specimens collected at the island of 

 Luzon. The largest of these Philippine examples is 2f mm. long, 2^ high, and 2 in 

 diameter. 



