45 



Diagnosis. A beautiful big white shell, well curved, tapering. Sculpture : 20 — 35 

 fine riblets at apex, separated by wider intervals. Intervals flat and shallow, microscopically 

 longitudinally striated, seen under a strong lens. Longitudinal sculpture very distinct for about 

 one fourth to one third the shell's length (in young specimens four about the half) losing anteriorly 

 in prominence but remaining superficially visible over some length. Anterior half or third of the 

 shell quite smooth, brilliant white, with oblique growth striae only. Apex often entire, but also 

 with a slit; anterior aperture circular. thin edged, generally oblique, parallel to the growth lines. 

 Length 65 mill., diam. of aperture 7 mill. 

 Length 51 mill., diam. of aperture 5 mill. 

 Length 50 mill., diam. of aperture 4,5 mill. 

 Length 45 mill., diam. of aperture 4 mill. 



D i s t r i b u t i o n. Off Colombo, Ceylon in Ó75 fms; Bay of Bengal in 597 fms. (Investigator). 



Remarks. The specimens obtained by the Investigator and described by Mr E. A. Smith 

 were only the apical parts of the shell. Aftervvards entire specimens were brought to the British 

 Museum which have been identified with tisitatuni by Mr E. A. Smith. The Siboga specimens 

 proved on comparison to be the same. Of those, four have a well-developed .slit measuring in 

 one 3 mill.; the others have the apex entire. 



53. Dentalmm amtissinium Watson. PI. II, fig. 39. PI. V, figs 9, 10, 11, 12. 



1879. Dentalinni acutissimum Watson, Journ. Linn. Soc. Lond., vol. XIV. 



1886. Dcntaliuin acutissimum Watson, Challenger Report, p. 8, pi. i, fig. 8. 



1897. Dentalmm acutissimum Watson. PiLSBRV & Sharp, Man. of Conch. vol. XVII, p. 94, 

 pi. 20, fig. 26. 



Stat. 88. o°34'.6N., 119° 8'. 5 E. Celebes Sea. 130 1 Metres. Fine grey mud. 12 Spec. 

 Stat. 211. 5°4o'.7S., I20°45'.5 E. Banda Sea. 1158 Metres. Coarse grey mud. 4 Spec. 

 Stat. 300. io°48'.6S., I23°23'.i E. Timor Sea. 918 Metres. Fine grey mud. 2 Spec. 



Diagnosis. Shell long and much attenuated, rather straight and very regularly curved, 

 very thin, brilliant and glassy. Sculpture: The surface is cros.sed by fine, sharpish, irregular 

 striae, which run very elliptically round. In the young shell the surface is regularly and finely 

 scratched by a great number of close-set, regular. sharp and extremely minute lines, which 

 very gradually become more and more faint, but are still traceable even in the full-grown shell. 

 The color is pure white, transparent, and almost hyaline in the fresh shell, but in the dead 

 shell the interior (not, as usual, the exterior) layers of the shell become opaque and chalky. 

 The edge is very thin and irregularly broken. At the apex the end is abruptly broken off in 

 one specimen, and in the other there is an irregular fissure with an internal lining process. In 

 one specimen from Station 246, which is full-grown, but very short, a large, thin, irregularly 

 shaped process projects, which, being obliquely cut off somewhat across the shell. supplies the 

 anal orifice. 



Length 1,52 inch, of young specimen from Station 218; breadth at mouth 0,12, at apex 

 0,026 inch. Length 1,14 of old and broken specimen. Station 246; breadth at mouth 0,23, at 

 apex 0,14 inch. (Watsox). 



