On Aquatic Carnivorous Coleoptera or Dytiscide. 691 
I. 73.—Genus RHANTATICUS. 
Coxal lines obliterated, so that no supra-articular border is visible, middle femora 
with quite short spinules. Elytra yellow speckled with black, the black specks 
being more or less coalesced to form two or three irregular transverse black fascia. 
A single species* is known; it hasa wide distribution in the warmer parts of the 
eastern hemisphere. 
1083. Hydaticus signatipennis, Lap., M.C.—Ovalis, fere angustus, parum con- 
vexus, levigatus, nitidus, testaceus, capite prothoraceque anterius et posterius in 
medio nigro-signatis, elytris nigro-irroratis, irrorationibus in fascias duas, una ante 
altera post medium, condensatis. Long. 93, lat. 5 m.m. 
In the male the anterior tarsi are large, and clothed beneath with well developed 
palettes; the more basal one of the three larger of these is distinctly larger 
than the other two, which in fact are about intermediate between it and the smaller 
ones ; the middle tarsi are not incrassate, but the three basal joints bear beneath 
two rows of small sessile palettes. 
The species is the smallest of the Hydaticides, and has much resemblance to a 
Rhantus; it varies in the extent of the black marks on the head and thorax, these 
are usually more largely developed in the individuals from Australia and New 
Caledonia than in those from other localities. In what may be called the type form 
(from tropical Asia) the vertex is black and the black colour extends forward along 
the inner side of the eye, while on the middle of the head there are two black marks 
placed at an angle to one another, and often joined so as to form a single angular 
mark; on the thorax the black marks in front and behind have but a small extension 
even in the lateral direction, and in some individuals the anterior one entirely 
disappears: in the Australian individuals there is an additional black transverse 
mark on the head in front of the other two, and in front of the basal mark of the 
thorax there is another black mark, which however is joined to the basal mark in 
the middle and at the sides so as to form a single transverse mark enclosing two 
yellow spots, which however are sometimes absent owing to the still greater exten- 
sion of the black colour. I can find no other characters to distinguish this form 
and can scarcely think it constitutes a distinct species. In the Australian form the 
hind tibize and tarsi are more or less black. The individuals from Madagascar show 
a reproduction of the markings of the Australian race but in a far less constant 
manner, and they have not the hind tibiee and tarsi dark, their form is shorter and 
the black fascize of the elytra less distinct than in the Australian individuals ; the 
* It is probable that H. congestus, Klug, (No. 1309 huj. op.) from Madagascar, is either a variety of this - 
species or a closely allied one. 
TRANS. ROY. DUB. SOC., N.S., VOL, 4U 
