17 



strong-, broad, strongest teeth near outer end of anterior séries; anterior séries consisting of ii, 

 posterior of 6 teeth, both séries only slightly arched. Shell of light brownish-yellow colour, nacre 

 dirty pearl white. 



Measurements of Holotype : — Length 5.4 mm., height 4 mm., diameter 2.5 mm. 



Habitat: — The Holotype and a right valve were brought up in a trawl at St. 178 

 (2° 40' S., 1 28° 37^5 E., 835 mètres). 



Remarks : — The solid and thick shell of a trigonal elliptical shape and very strong 

 hinge are characteristic of aV. (iV.) pachydonta. 



9. Nucula [Niccula] niuibosa sp. nov. (Plate I, figs. 11, 12). 



The following is a description of this new species : — Shell small, trigonal, inequilateral, 

 ventricose, thin ; escutcheon not very greatly depressed, subcordate ; apex acute, umbones slightly 

 tumid, curved inwards and backwards, almost approximating in middle line ; anterior side sloping, 

 lightly convex, acutely rounded towards the arched basai margin ; posterior side shorter, forming 

 an acute angle with the basai margin ; sculpture consisting of fine concentric rugae and microscopic 

 radial lines ; hinge-plate weak, teeth moderately strong, anterior séries consisting of 8, posterior 

 of 5 teeth, both séries slightly arched. Shell of light yellow colour, nacre dull pearly white. 



Measurements of the Holotype: — Length 3.2 mm., height 2.8mm., diameter 1.7 mm. 



Habitat: — A single shell of this interesting species was trawled at St. 211 (5° 40^7 S., 

 i20°45'.5E., 1158 mètres). 



Remarks : — The characteristic trigonal form and the weak hinge-plate, consisting of 

 few teeth in both séries, distinguish N. [N^ nimbosa from the other allied species, 



10. Nucula {Nucula) datttzenbergi sp. nov. (Plate I, figs. 13 — 16). 



The following is a description of this new species : — Shell médium sized, obliquely 

 ovate, very inequilateral, subcompressed ; escutcheon area moderately depressed, narrowly heart- 

 shaped ; umbones acute, not very tumid, hardly prominent, curved inwards and backwards ; 

 posterior side much shorter than anterior, nearly straight, anterior very convex ; ventral margin 

 arched ; sculpture consisting of regular, concentric, minute striae ; hinge-plate moderately strong, 

 anterior séries with 14, posterior with 7 teeth, both séries slightly arched. Shells of a brownish yellow 

 colour, but greater part of shells bleached whitish and without periostracum, nacre shining white. 



Measurements: — Length 10.4mm., height 8.8mm., diameter 4.5 mm. 



Habitat: — The Holotype and a left valve were dredged at St. 59 (Western Entrance, 

 Samau Strait, 390 mètres) and a younger shell at St. 52 (9°3^4S., ii9°56^7E., 959 mètres). 



Remarks: — This species, which I hâve associated with the name of the famous French 

 Conchologist, Monsieur P. Dautzenberg, bears a superficial resemblance to N. (iV^.) obliqua Lam., 

 but the new species is easily separated by its distinctive hinge structure and its fine sculpture. 



11. Nucula i^Acila) mirabilis Adams & Reeve. 



1850. Nucula mirabilis Adams & Reeve, "Samarang" Moll., p. 75, pi. XXI, fig. 8. 

 1858. Nucula [Acila] mirabilis Adams, H. & A., Gen. Rec. Moll., p. 545. 



SIBOGA-EXPEDITIE LIIIi:. 3 



