270 THE VOYAGE oK II. M.S. CHALLENGER. 



v;ilde iiuvquihiteralis, sordide alljidii, siilipellucida, crassiuscula, parimi couvexa, postire 

 rotundata, striis incremeuti minutis sculpta, lineisque albis conspicuioribus numerosi.s 

 radiantibus curvatis ornata. Margo dorsi auticus brevissimus, leviter concavus, declivis, 

 posticus elongatus, arcuatus, horizontalis. Margo veutris parum convexus, antice lente 

 ascendens. Umbones couspicue antrorsum involnti, baud coutigui, iu :|; lougitudiuis 

 collocati. Linea cardinalis pone umboues arcuata, in valva sinistra sulco elougato arata, 

 dente unico crassissimo ab apice fossa profunda separato munita. Pagina interna 

 uitida, striis radiantibus notatis. Cicatrices et linea pallii baud conspicuae. 



Only two left valves of this curious little sbell were obtained. Tbej" are very inequi- 

 lateral, the anterior side being very short, acuminated or beaked, the posterior on the 

 conti'ary terminating in a broadly rounded extremity. They are thickish in substance, 

 suljpellucid white, not very convex, rather deeply concave in front of the umbo. They 

 are sculptured with very minute strijB of growth, and one of them is further ornamented 

 with numerous curved radiating lines which appear opaque-white upon a somewhat 

 diaphanous ground, and are closer together down the posterior half of the surface than in 

 front. The anterior part of the doisal line is very short, oblique, and slightly concave, 

 the posterior, on the contrary, being long and horizontally curved. The ventral or lower 

 outline is scarcely at all excurved, and gently ascends towards the front. The umbo is 

 remarkably curved over anteriorly, and being also directed at the tip away from the 

 dorsal edge, would not touch that of the opposite valve when closed. The hinge-plate 

 behind the beak exhibits a long, slightly curved groove for the reception of the ligament, 

 and a single very strong tooth, cleft at the top, rests upon the anterior part (beneath the 

 umbo), which is separated from the posterior portion by a deep broad concavit3^ The 

 interior is glossy and marked with the external radiating lines. Neither the muscular 

 scars nor the pallial line have been discovered. 



Length if mm., height 1^, probable diameter of complete shell 



Habitat. — From the Reefs off Honolulu, Sandwich Islands, at a depth of 40 fathoms 

 (Challenger) ; Sandwich Islands (Gould) ; Reunion or Bourbon (Deshayes). 



One of the two valves obtained at this locality is destitute of the radiating white 

 lines, and is less acutely beaked in front. Excepting the absence of the green colour, so 

 characteristic of this curious shell, the presence in one instance of more numerous radiating 

 white lines and the small size (due probably to difference of age) there does not appear 

 at present any sufficient reason for considering the valves described above as specifically 

 distinct. The want of colour may be the result of fading, and the extra acuteness of 

 the rostrated end in one of the valves an unusual variation, as neither in Deshayes' figure, 

 nor in specimens in the British Museum, does this part appear quite so acuminate. 



The true systematic position of this curious genus has yet to be determined. Gould 

 associated it with Pedum and Vulsella, whilst Deshayes placed it with the Mytilidse. 



