39 



is rather lighter in colour, but presents all the same characters confirming the specific importance 

 of the chief characteristic, which might otherwise have been thought accidental (Sowb.). 



A young specimen was obtained measuring 30 mill., with a greatest diam. of 5 X 4,3 miH- 

 (lateral diam. first). It shows only the well curved apical part of the fuU-grown shell. It is whitish 

 with regular transverse bands of light brown; the ribs are irregularly impressed by the growthlines 

 and there is a narrow slit measuring 2,7 mill. 



45. Dentalium Sibogae n. sp. PI. IV, flgs 17, 18. 



Stat. 159. o°59'.iS., I29°48'.8E. 411 Metres. Coarse sand. i Spec. 



Diagnosis. A big wide shell, totally straight but for a hardly perceptable 

 inclination at the top; trigonally compressed, the "excurved" side flat, the 

 "incurved" side with one very obtuse angle. Sculptured with numerous subequal 

 riblets, very like D. Hungerfordi. Apex with a long slit, measuring 8,5 mill. 

 Anterior aperture trigonal, the angles rounded. Length 70 mill. ; dorso-ventral 

 diam. of anterior apert. 10 mill. lateral diam. 15 mill., diam. of apex 2,2 mill. 



Fig. 22. Ant. apert, 

 of D. Sibogae. 



Remarks. Sibogae is nearly related to Hungerfordi. The difference lies in the shape, 

 Sibogae being quite flattened on the excurved side, while in Htingerfordi that side is convex. 



Subgenus Tesseracme Filsbry & Sharp 1898. 

 1897. Tesseracme Pilsbry & Sharp, Manual of Conch., vol. XVII, p. 249. 



Small or moderate sized shells with the tube square at and near the apex, having angles 

 on the convex, concave and two lateral sides, becoming subcircular at the aperture. Generally 

 costulate between the angles, sometimes smooth; the apical orifice occupying a short pipe, or 

 without this and square or round (P. & Sh.). 



Key to Species. 



I. The four primary ribs bifid or trifid dispar. 



II. The four primary ribs serrate quadricostatum. 



III. The four primary ribs not split or serrate. 

 a. Intervals smooth. 



b. 2,2 riblets at aperture, greatest diameter about i r times the length. dipsycha. 



b' . 36 riblets at aperture, greatest diameter about 6 or 7 times the length. quadrapieale. 

 a'. Intervals striated tetrapleurum. 



46. Dentaliuvi dispar Sowerby. PI. II, figs 22, 23. 



1860. Dentalium dtspar Sowerby, Thes. Conch. III, p. 103, pi. 224, fig. 37. 

 1872. Dentalium dispar Sowerby, Conch. Icon. XVIII, pi. 4, fig. 25. 



