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



Of this sj5ccies only two left valves are at present known. These, although of very- 

 small size, are ajiparently adult, judging from their thickness of structure, the denticulate 

 inner margin, and the strong character of the hinge. It is a species of an oblique ovate 

 or rounded growth, rather strong for so small a form, moderately convex, excavated in 

 the lunular region, and a little depressed down the posterior slope. It is white, somewhat 

 inequilateral, broadly rounded in front, narrower behind. The sculpture consists of 

 strongish, rather elevated concentric riblets somewhat narrower than the interstices 

 between them, which exhibit excessively fine radiating lirse. The beaks are rather large, 

 prominent, curved over towards the front, and not very acute. The lunule is deeply 

 depressed, somewhat indistinctly defined by a raised edge and sculptured by the fine 

 extremities of the concentric ridges. The left valve has two cardinal teeth and the right 

 probably the same number. They are strongish, about equal in size, and diverging. 

 The anterior is erect, beneath, or very slightly in front of, the tip of the umbo and free 

 from the dorsal edge, the posterior being directed backwards, and perhaps a trifle 

 slenderer. The lateral teeth are strongly developed, and about equidistant from the 

 beak. The ligament is totally internal, elongate, narrow, and placed in a deep groove 

 below the dorsal margin behind the posterior cardinal tooth. The inner edge of the 

 valves, with the exception of that portion occupied by the hinge and lateral teeth, is 

 minutely denticulated. The muscular scars are fairly well defined, the pallia! line simple, 

 and the inner surface of the valves dull, under the microscopic appearing rather rugose. 



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



Habitat. — Off Levuka, Fiji Islands, in 12 fathoms. 



This is a remarkable little shell on account of its obliquity, the expanded anterior end, 

 the strong hinge, and denticulate margin of the valves. It differs in the last mentioned 

 character from Lucina quadrata, Angas, a species found at Port Jackson which has a 

 somewhat similar form and the same hinge-characters, but is diflferently sculptured 

 externally. 



Lucina (Codakia) congenita, n. sp. (PI. XIII. figs. 7 -7a). 



Testa Lucince levuhance similis, sed minus obliqua, liris concentricis validioribus, 

 radiantibus fortioribus, lunula breviori instructa, margine valvarum interuo crassiori, 

 donticulis majoribus munito. 



This species bears considerable resemblance to Lucina levukana, but may be distin- 

 guished by its less oblique form, the anterior side being less produced and not so 

 expanded. The posterior side of the valves displays more of a depression, the lunule is 

 shorter, and consequently the front dorsal margin is more briefly excavated. The 

 umbones in this species are hardly so peaked, the concentric lirse a good deal thicker 



