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



naintiug is so faint that, at a short distance from the eye, it is scarcely observable. 

 The valves are moderately strong, and finely, concentrically striate and sulcate. The 

 umbones are smallish, moderately acute, white or pale reddish, curved over towards 

 the front, and situated at about one-fourth of the entire length from the extremity. 

 The lunule is smallish, elongate, heart-shaped, scarcely at all sunken, a little elevated 

 alono- the central line, circumscribed by an impressed line and striated Ijy the lines 

 of growth. The dorsal margin descends considerably on both sides of the beaks, 

 the anterior portion being almost rectilinear, and the posterior much longer, and 

 I'egularly, gently arched. The lower outline is Ijroadly arcuate, more ascending in 

 front than behind, forming with the upper margin subequal, sharply rounded, lateral 

 extremities. The hinge is rather strong for so small a shell, having in the left valve 

 a stout triangular central tooth and a largish elevated and somewhat compressed 

 lateral. The front muscular impression is ovate-suljp}'riform, and smaller than the 

 posterior, which is more rounded. The sinus in the pallial line is moderately deep, 

 wide, and has a squarish aspect as the end is obliquely truncated, the iimer angle 

 being acute and almost reaching the centre of the valves. 



Length 13 mm., height 10^, diameter 7. 



Habitat. — Torres Strait, in 3 to 1 1 fathoms (Challenger) ; Port Molle, Queensland, 

 at a depth of 14 fathoms {Dr. Coppinger in Brit. Mus.). 



Cijtherea minuta, Koch (Philippi's Abbild., vol. i. p. 200, pi. iii. fig. 8), is a more 

 ecpiilateral species than that under consideration, has a larger lunule, and a narrower 

 and somewhat deeper pallial sinus. 



The specimens from Torres Strait are almost entirely white, with the exception of the 

 reddish apices of the umbones, but this absence of painting may or may not Ije usual. 



Cythereu (Carijatis) regularis, n. sp. (PL I. figs 8-86). 



Testa parva, inasquilateralis, parum inflata, alba, sul)tenuis, trigono-rotundata, 

 conceutrice regulariter ac tenuiter lii-ata, lunula magna, baud profunda instructa. 

 Umbones promineutes, incurvati, latus anticum versus curvati, concentrice tenuiter 

 striati, alicpianto ante medium siti. Margo dorsalis posticus elongatus, curvatus, 

 obliquus ; anticus brevior, minus arcuatus, obliquior ; ventralis late rotundatus. Latus 

 anticum latins quam posticum. Pallii sinus triangularis, profundus. 



This species is a little longer than high, somewhat inequilateral, and inflated, 

 thinnish, white, subtrigonal, rounded, a little produced and narrower liehind than in 

 front, sculptured with regular, fine, concentric narrow grooves and intervening rounded 

 Yivse, very slender at first, and increasing in thickness with the growth of the shell. The 

 uml)ones are well produced and incurving towards the front and situated decidedly in 

 advance of the centre. The lunule is large, cordate, not sunken, and is marked off by 



