214 Rey. H. Clark on the Dytiscidee 
XVI.—Catalogue of the Dytiscidee and Gyrinide of Australasia, with 
Descriptions of new Species. By the Rev. Hamer Crark, M.A., 
F.L.S. 
Parr III. 
I propose in this paper to examine one of the sections of Gyrinide, 
the genus Enhydrus, so far, that is to say, as ite Australian repre- 
sentatives. The genus itself was founded on a magnificent species 
peculiar to Brazil, Z. sulcatus, Wied., which is the only species foreign 
to Australia. It is seldom, indeed, that links are met with connect- 
ing Australia with South America, and so we are not surprised to 
notice that this connecting link is not of the closest. Undoubtedly, as 
to all important characters, #. sulcatus may be placed in the same 
group as the following species ; and yet how unlike the insects are 
in general form and appearance! . sulcatus is large, peculiarly 
depressed, and broadly ovate: the Australian species are entirely 
different, considerably smaller (some not more than one-third of the 
size), narrower, and more parallel. 
The genus is closely connected with Giyrinus by the presence of a 
scutellum : it is separated from it simply by its general form, and 
by the much greater length (in proportion) of the anterior legs. Dr. 
Aubé seeks to establish a distinction also in the length of the labial 
palpi: this sometimes obtains, but seems, so far as it has any value, 
to be a specific rather than a generic character. The diagnosis of 
Professor Lacordaire is based chiefly, if not entirely, on the length of 
the anterior tibiz ; and this, with a consideration of the general form, 
will, I think, hold good: the outline (if we may except the Brazilian 
type, E. sulcatus)is more parallel and more elongate than that gene- 
rally of Gyrinus proper. I include in the group (following M. La- 
cordaire) HE. oblongus of Aubé, but this is the extreme limit of the 
form: it is just possible that ultimately this last species may be 
separated from Enhydrus (in which it was placed by Brullé), and 
again reunited, as intended originally by Boisduval, with Gyrimus. 
If we accept the definition of the genus as thus laid down, that is 
to say, scutellated Gyrinide with elongated anterior legs and narrow 
subparallel forms, we find that the Australian species group them- 
selves naturally, and yet not without manifest connecting links, with 
Gyrinus, as EL. oblongus, Reiche. The characters which are of appa- 
rently special value in the separation of the species of this group inter 
se are (of course) the outline of form, the depth and determinateness 
of the channels of the elytra, the size and figure of the scutellum, 
and the sinuations of the apical part of the elytra. None of these 
