OPISTHOBKANCHIATA FROM THE ABKOLHOS ISLANDS. 567 
As [)ointed out in the passage quoted above, only three species o£ this 
remarkable genns have been recorded : namely, jV. citrina Bergh from Earo- 
tonga by a single specimen, iV. minor Eliot from Chuaka on the east coast of 
Zanzibar by a single specimen, and JV. gardineri Eliot from the Maldive 
Islands also by a single specimen. 
In spite of certain minor differences^ i. e. the presence of black spots, the 
presence of a Y-shaped arrangement of small tubercles on the dorsum, the 
absence of labial armature inter alia in Eliot's specimen, I have no 
hesitation in referring the present form to his species, N. garditieri. The 
size is about the same, the teeth similar, the valved rhinophoral aperture 
similar, and also the branchial valves with their elaborate spatulate 
processes. 
As will be seen the genus is very little known, and it is to be hoped that 
sufficient material for a detailed investigation of its structure will be forth- 
coming. It apparently contains three distinct species : — - 
N. CITRINA Bergh. — Pale yellow ; somewhat broader ; 7 quadripinnate 
gills ; gill-valve with 8 points more than one-third of the way for- 
ward ; valved rhinophoral aperture ; radula 56 vows typically 
14 . .4, tooth with indication of third blunt denticle. 
N. GARDINERI Eliot. — Chrome-yellow with or without black spots, 
narrower ; numerous tiny gill-plumes ; gill- valves marked, three in 
number, furnished with spatulate processes, about halfway back ; 
valved rhinophoral aperture ; radula 56-58 rows typically (34-42) . 
. (34-42), tooth with only second blunt denticle. 
N. MINOR Eliot. — Lemon-yellow sharply marked with black lines, 
narrower ; 27 small tufts of gills in three areas ; gill-valves three in 
number, inconspicuous, simple ; radula 33 rows typically 25 . . 25, 
tooth not nearly so distinctly denticulate as in foregoing species. 
These differences appear to warrant the retention of the three forms as 
valid species. 
Genus Nembrotha Bergh, Malakol. Unters. TIeft xi. p. 450 (1877). 
Type here designated, N. nigerrima Bergh. 
The body is limaciform, nearly smooth ; dorsum not differentiated from 
sides ; the rhinophores are retractile with a perfoliate clavus ; the branchias 
are paucifoliate and bi- or tri-pinnate ; the tentacles are short and lobate ; 
the foot is quite narrow. The labial armature is inconspicuous or absent. 
The radula fairly narrow ; the rachidial tooth is depressed, subquadrate, or an 
armed curve ; the first pleural tooth is large and falciform, and the several 
external teeth are depressed. 
