REPORT ON THE LAMELLIBRANCHIATA. 187 



Of this species only a siugle left valve is at present knowu. It is roundish, white, 

 about equilateral, moderately convex, not very solid, and sculptured with fine elevated 

 concentric lines (which are scarcely large enough to be termed lamellse) crossed by 

 numerous not very apparent radiating substrise. There is a slight narrow lunular 

 depression, causing the anterior dorsal slope to be faintly concave. The hinder margin 

 is short, straight, and hardly at all oblique, rounding off somewhat squarely into the 

 side margin, which is more obtuse and less curved than the anterior side. The umbo 

 is small, peaked, curves over towards the front, and rises a little above the hinge-line. 

 In this valve there are two distinct, divergent, cardinal teeth, which are unequal in size, 

 the front one being more than double the size of the other, and obliquely sloping 

 towards the anterior end. There is a not very strongly developed posterior lateral 

 tooth, separated from the outer margin by a shallow groove, which, no doubt, receives 

 a corresponding tooth in the other valve. The ligament is totally internal and situated 

 in a deep, narrow, oblique furrow, beneath the hinder dorsal mai'gin. The interior is 

 dull, with the exception of that portion of the surface outside the pallial line which is 

 glossy. Towards the middle there are traces of radiating strias, and the outer edge is 

 very finely denticulated. 



Length 5 mm., height 4^, probable diameter of the complete shell 2f. 



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



This species closely resembles Luclna jacksoniensis, but is less distinctly radiately 

 striated. 



Cryptodon, Turton. 



This genus was founded in 1822 by Turton^ for the reception of the Tellina 

 Jlexuosa of Montagu. It is considered by some authors identical with Axinus of 

 Sowerby. If this really be the case the latter name should be adopted, as it was 

 published a year before Cryptodon. It appeared in the fourth volume of the Mineral 

 Conchology, which bears on the title-page the date 1823. This, however, only refers to 

 the completed volume, for this work was published in parts, and that containing 

 plate 315, on wdiich the type {Axinus angulatus) is figured, was issued in 1821. Both 

 Agassiz' and Herrmannsen^ quote the date of the volume as that of the publication 

 of this genus, and no doubt this has misled Messrs. Adams and Chenu into adopting 

 the name proposed by Turton. 



As far as I can ascertain, the hinge of Axinus angulatus has never been described, 

 for the shell associated with it by Nyst * seems to me distinct. 



Such being the case, I prefer employing the name Cryptodon, foi-, although 



1 Conch. Inst. Brit. Dithyra, p. 121. ^ Nomen. Zool., Index universalis, p. 42, Mollusca, p. 10. 



^ Indicia geu. nialacol. prim., vol. i. p. lt)(). ^ Coq. et Polyp, foss. terr. tert. Belj^ique, p. 140. 



