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



the hinge-line, slightly eroded at the tip, and situated at about three-eighths of the 

 entire length from the hinder extremity. The hinge-plate is absolutely toothless, and 

 only very slightly thickened on both sides. The internal ligament is small, yellow, 

 and, starting from beneath the tip of the beaks, extends about a millimetre backwards. 

 The interior of the valves is moderately shining, feebly substriated in a radiating 

 direction, and, under the microscope, appears to be minutely rugose. The muscular 

 scars and pallial impression are too indistinct for description. 



Length 16 mm., height 12, diameter 6. 



Habitat. — Station 133, South Atlantic, in 1900 fathoms; Globigerina ooze. 



This shell is unusually thin for a Lucinid, and the hinge is very delicate, as might 

 be expected in one from such a great depth. 



? CryiDtodon barhatus (Reeve). 



Lndiia hatiiata, Eeeve, Conch. Icon., vol. vi. pi. iv. figs. 16, a, h. 

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



A single left valve, all that was obtained, agrees exactly with this species in form, 

 the toothless character of the hinge, the position of the ligament, the form of the 

 muscular scars, and in the small deep lunule. The external concentric lines of gro\\i;h 

 are, however, rougher to the touch and apparently more raised, and the shallow 

 depression down the posterior side is a little nearer the dorsal margin. 



Cryptodon falklandicus, n. sp. (PL XIV. figs. 3-3«). 



Testa rotundata, mediocriter convexa, paulo iutequilateralis, alba, cretacea, epidermide 

 tenui flavescente induta, concentrice striata. Valvse tenues, sulco postico lato radianti 

 haud profundo arataj. Margo ligamenti leviter arcuatus, anticus declivis, rectiusculus. 

 Latus anticum ad extremitatem rotundatim subangulatum, posticum breviter truncatum. 

 Pagina interna alba, parum nitida, plus minusve rugosa. Cicatrix antica. magna, 

 elongata, irregularis, posterior minor, brevior. 



This species is a trifle longer than high, roundish, moderately convex, thin, white, of 

 a chalky appearance, and covered more or less with a thin yellowish epidermis. It is 

 somewhat inequilateral, the beaks being situated a little in advance of the centre, and 

 striated rather roughly by the lines of growth. The valves exhibit a broadish shallow 

 depression down the posterior side, which produces a short truncated extremity to the 

 margin. There is also a faint depression ou the opposite side, marking off an elongate 

 cordate lunular space. The posterior or bgamental portion of the dorsal margin is a 

 little curved and less oblique than the anterior, which is straightish, and joins the upcurv- 

 ing ventral outline almost in a rounded angle. The hinge-line is thickened slightly to 



