REPORT ON THE LAMELLIBRANCHIATA. 



147 



in medio valvarum subobsoletis instructa ; margo dorsi anticus brevis, obliquus, vix 

 arcuatus, posticus lougior, superne aliquaiito curvatTis, longe dcsoondcns. Margo vcntris 

 late arcuatus, postice indistiucte subsinuatus. Umboues promincntes, bene incurvati, 

 apice rufescentc. Lunula parva, late cordiformis, linea elevata rufo picta circumscripta. 

 Dentes fere ut in Circe picta. Pagina intern;i jihis minusvc fuseo tincta. Cicatrices 

 parvse, antica elongata, subovata, postica rotuudata. Sinus palHi l)i'evis. minime 

 profundus. 



This species is moderately intiated, very inequilateral, entirely white or ornamented 

 with a few transverse zig-zag brown lines. It is somewhat trigonal in form, much 

 broader in front than behind, where it is somewhat rostrate. The surface is glossy, 

 regularly concentrically finely sulcate upon the beaks, and more coarsely at the sides, 

 the grooves upon the central portion of the valves becoming more or less obsolete. The 

 ridges are broader than the sulci which separate them, and rounded, especially those 

 upon the beaks, which gradually increase in thickness from the apex. The umbones are 

 considerably elevated, well curved over towards the anterior end, and terminate in a 

 brown or reddish apex. The dorsal line is straightish in froiit, ohlique, a little arched at 

 first behind the umbones, then more rectilinear, prolonged, and much descending. The 

 lower margin is broadly curved, indistinctly subsinuated towards the posterior end, 

 more arcuate and upcurving in front. The lunule is small, broadly cordate, and enclosed 

 with a fine elevated line which is bordered on the outside with a few short, reddish 

 lines. The hinge is very similar to that of Circe picta. The interior is sometimes 

 almost entirely white, l)ut in other specimens is more or less stained with brown. 

 When present this colour occui's chieflv aliout the middle of the valves below the 

 umbones or down the posterior side, biit never in front, judging from the four specimens 

 under examination. The muscular impressions are small, the anterior one being- 

 elongate and oval, and the hinder one broader and subpyrifdini. The sinus in the 

 pallial line is small and very shallow. 



Length 15^ mm., height 13f, diameter 10. 



Habitat. — Off Levuka, Fiji, in shallow water, and 12 fathoms. 



On comparing young specimens of Circe picta, and one or two allied forms, it will 

 be found that they are very different in form from tlie present species. They are 

 much more regularly oval, and about as broad liehind as in front, whilst in Circe 

 gordoni the posterior end is conspicuously narrowed. The umboues too in the latter 

 are more elevated, the concentric sculpture upon them decidedly stronger, and the 

 lunule is much shorter and broader. In Circe picta it is generally stained with blackisli- 

 brown in front of the beaks, Imt in the .species under consideration it is probably 

 always white. 



/C 



