15 



arched than is shown in Smith's figures. The measurements of the largest spécimen obtained 

 by the "Investigator" were 15 mm. X i i rnm. X 7-5 nim., while those of the largest shell obtained 

 by the "Siboga" Expédition are: — 18 mm. X 15 nim. X 9-8 mm. 



Distribution: — The types of N. {N.) donaciformis were collected at St. 165 in the 

 Arabian Sea off the Coromandel Coast from a depth of 145 — 250 fathoms. 



The "Siboga" Expédition obtained several spécimens from St. 27 (8°43'.5 S., ii5'2i.5 E., 

 210 mètres), St. 87 (o°32^S., ii9°39'.8E., 655 mètres), and St. 178 (2°4o'S., 128° 37.5 E., 

 835 mètres). 



4. Nticula [Nîtcula) rugifera sp. nov. (Plate I, figs. i, 2). 



The following is a description of this new species : — Shell small obliquely wedge-shaped, 

 inequilateral ; solid, slightly inflated ; escutcheon greatly depressed, cordate ; apex obtuse, umbones, 

 moderately tumid : anterior side nearly straight, posterior angulate, anterior end subtruncate ; 

 sculpture consisting of fine concentric rugae and about 10 much stronger transverse ridges on 

 the anterior slope, hinge-plate narrow, teeth strong, anterior séries consisting of 16, posterior 

 of 6 teeth, anterior séries almost straight, posterior distinctly arched. Shell of a dirty yellow 

 colour, nacre dull pearly white. 



Measurements: — Length 5mm.: height 3.8mm.; diameter 2.5mm. 



Habitat : — A single spécimen, the Holotype of the species, was brought up in a deep-sea 

 trawl at St. 173 (3°27'.oS., i3i°o'.5E., 567 mètres). 



Remarks : — The shape and transverse ridges on the anterior slope of the shell are 

 characteristic of N. (A^.) rtcgifera. 



5. Nttcula {Nucula) diaphana sp. nov. (Plate I, figs. 3, 4). 



The following is a description of this new species : — Shell médium sized, ovate, sub- 

 acuminate at both ends, inequilateral, ventricose, thin ; escutcheon concave, narrowly cordate ; 

 umbones acute, tumid, prominent, curved inwards and approximating in middle Une ; anterior 

 side longer and more arched than posterior; sculpture consisting of concentric very fine, microscopic 

 striae and a number of more impressed lines of growth ; hinge-plate strongly developed consisting 

 of closely packed teeth, anterior séries with 11, posterior with 7 teeth, both séries only slightly 

 arched. Shell of light horn-yellow colour, transluscent, nacre pearl white, iridescent. 



Measurements (in millimètres) : 



Holotype Paratype 



Length ....... 8 7.4 



Height 6 5.7 



Diameter 4.5 4.2 



Habitat : — Three spécimens of this interesting species were brought up in a trawl at 

 St. 52 (9° 3^.4 S., ii9°56'.7E., 959 mètres). 



Remarks : — Nticula [Nuculd] diaphana resembles N. {N.) cttmingii Hinds, but the 

 strong hinge and the very thin shell of the former distinguish it without any difficulty from 

 the latter. 



