51 



alike and fragments of both species, sliowing only the anterior parts, could easily be mistaken 

 for each other. Posteriorly however the difference is marked. In stapes the longitudinal angles 

 are much sharper, the arch on the conve.x side is narrower, and higher in proportion to the 

 flat face than in insolitttni, while the sides are less conve.K. Also in stapes the rate of increase 

 is smaller than in insolit/iiii. 



60. Dcntalhtiii pacJiypleuriiin n. sp. PI. V, figs 21, 22. 



Stat. 208. 5°39'S., 122° 12' E. Banda Sea. 1886 Metres. Solid green mud. 2 Spec. 

 Stat. 271. 5°46'.7S., i34°o'E. Arafura Sea. 1788 Metres. Bluish green mud of a uniform 



appearance, i Spec. 



Diagnosis. Shell very slender, moderately curved, smooth, white and brilliant, without 

 longitudinal sculpture ; cylindrical, but the convex side is very slightly laterally 

 compressed reminding one of forms like stapes and insolitzim. A transverse 

 section near the apex shows that the wall on the concave curve is thickened, Y\g. 26. 



which is also the case in the preceding species; there is however not the faintest Section near the apex 



of D. pachypleiirum. 



trace of longitudinal angularity. Apex thick-edged with a supplemental tube. 

 Growth striae hardly noticeable. Anterior aperture subcircular, thin-edged. 

 Length 46 mill., greatest diam. 2,4 mill. 

 Length 36 mill., greatest diam. 1,9 mill. 



6[. Dentalmm truncatum n. sp. PI. VI, fig. 33. 



Stat. 90. 1° I7'.5 N., 1 18° 53' E. Celebes Sea. 281 Metres. Coral sand and stones, i Spec. 

 Stat. 256. 5°26'.6S., 1 32° 32'. 5 E. Arafura Sea. 397 Metres. Greyish green mud. 2 Spec. 



Diagnosis. Shell slightly but evenly curved, cylindrical or faintly trigonally compressed 

 in the way of iiisotifuni. White and brilliant, nearly smooth but for some deeply 

 incised wrinkles near the apex. Apex faintly trigonal, strongly tn.ncated, thick- 

 edged with a minute orifice and a short supplemental tube. Anterior aperture 



Fig. 27. Apex 



subcircular, thin-edged, a little oblique. of D. truncatum. 



Length 18 mill., diam. of anterior apert. 1,5 of apex 1,4 mill. 



Length 16 mill., diam. of anterior apert. 1,6 of apex 1,1 mill. 



Length 23 mill., diam. of anterior apert. 2,3 of apex 1,4 mill. 



Remarks. All the specimens show deep irregular fissures where the shell alter breakage 

 has been repaired. The concentric lines near the apex remind one of the group of D. tracheatuni. 

 The specimen of Stat. 90 has them over its whole surface while the others are anteriorly quite 

 smooth with superficial growth striae only. 



Subgenus Laevidentalium Cossmann 1888. 



1888. Laevidentalium Cossmann, Ann. de la Soc. Roy. Malac. de Belgique, XXIII, p. 9. 

 1897. Laevidentalinni Cossmann. PlLSHRV & SHARP, Man. of Conch., vol. XVII, p. 97. 



Shell of moderate or large size, smooth, with growth lines only, circular or slightly oval in 

 section ; apex simple (typically), or with a short notch on the convex side as in Antalis. (P. & Sh.). 



