I 
504 
INSECTA. 
inclose themselves. According to Koesel, the eggs of the Dytisciis marginalis hatch ten or twelve 
days after being deposited : at the end of four or five more, the larva is already four or five lines long, 
and moults for the first time. The second change of skin takes place at the expiration of a similar 
interval, and the animal is now as large again as it was before ; when full grown it is two inches long. 
In summer it has been observed to become a pupa at the end of fifteen days, and a perfect insect in 
fifteen or twenty more days. 
This great genus is divisible as follows : — 
The majority have the antennae composed of eleven distinct joints ; the outer palpi filiform, or 
slightly thickened at the tips, and the base of the hind-legs exposed. 
Dytiscusy has all the tarsi composed of five distinct joints ; the three basal joints of the fore-legs being very 
large, and forming an oval or orbicular plate. Type, D. marginalisy Linn., a very common British species, an inch 
and a quarter long, being of a dark olive colour with a 
butf-coloured margin entirely round the thorax, and a 
line of the same colour on the outer margin of the elytra, 
which are not dilated at the sides; those of the female 
are furrowed from the base about two thirds of the whole 
length. Fabricius says, that the species when laid upon 
its back gains its ordinary position by taking a leap. 
Esper kept a specimen of this insect for three years and 
a half in good health in a large bottle of water, feeding it 
every week and sometimes oftener with bits of raw beef 
about the size of a nut, upon which it precipitated itself 
and sucked the blood entirely from it. It was able to fast 
Fiji. 55 -Dytiscus marginaiis and its larva. for a moiith at a time. It killed a specimen of Hydro- 
pMlus piceus, although as large again as itself, by piercing it between the head and thorax, the only part of the 
body without defence. According to Esper, it is sensible to the changes of the atmosphere, which it indicates by 
the heights at which it keeps in the bottle. 
Dytiscus Roeselii, Fab., [the type of Curtis’s genus Cybister, or Trogus of Leach], is much more depressed than 
the preceding, and has the outer margin of the thorax and elytra yellowish ; these elytra are finely striated in the 
female ; the hind legs have the tibiae very short and broad. It is found in the neighbourhood of Paris and in Germany, 
but is extremely rare in England. 
Dytiscus serricornis, Paykull, is vei'y remarkable for the antennae of the male having the four terminal joints 
forming a compressed and toothed mass, whence Dr. Leach formed it into his genus Agahus ; other characters, 
such as the form and relative proportions of the joints of the outer maxillary palpi, have also led him to form other 
genera, namely — Hydaficus {Dyt. Hybneri, transversalis, &c.) and Acilius (D. sulcatus)^ [These various groups, 
here reduced by Latreille to the subgenus Dytiscus, are far better marked than many of the groups admitted amongst 
the Carabiques possessing characters, not only in the imago, but also in the larva states, amply sufficient to warrant 
their separation.] 
Colymbetes, Claiv., has all the tarsi distinctly 5-jointed, but the four anterior tarsi in the males are equally dilated 
into one small oblong plate, and the antennae are at least as long as the head and thorax ; the body is perfectly 
oval, and broader than deep, and the eyes are not exposed. Types, Dyt. fuscus, Panz., D. cinereus, Fabr., Panz., 
&c. [These insects are of an intermediate size between the foregoing and following species, and form a very exten- 
sive group. Erichson, Eschscholtz, and Aub^, have particularly studied this group, and have proposed various 
dismemberments from it, which have been partially adopted by more recent authors.] Some of the smaller species 
without a visible scutellum, and with the anterior tarsi scarcely dilated in the males, compose Leach’s genus 
Laccophilus ; such are the D. kyalinus. Marsh., D. minutus, Linn., &c. 
Hygrobia, Latr. {Hydraclina, Fabr., Pcelobius, Schonh.), have the four anterior tarsi in the males also equally 
dilated into a small oblong plate, but the antennae are shorter than the head and thorax ; the body is ovoid, very 
thick in the middle, and the eyes very prominent. Type, H. Hermanni, Latr., [a common British species]. 
Hydropoms, Clairv., has the four anterior tarsi spongy beneath in both sexes, with only four distinct joints, the 
ordinary fourth joint being obsolete or very small, and hidden, as well as the base of the following, in a deep notch 
of the third. The scutellum is not visible. The body is oval. Types, Dytiscus inequalis, picipes, &c. 
Hyphydrus, Latr., consists of such species of the latter as have the body nearly globular, and the last joint of the 
four anterior tarsi is very small, and scarcely extending beyond the preceding. H. gibba, ovalis, scripta, Fabr. 
Noterus, Clairv., differs from all the preceding by having the antennae dilated in the middle, and the last joint of 
the labial palpi is notched, so as to appear forked. Dytisciis crassicornis, Fabr. 
Haliplus, Latr., (Hoplitus, Clairv., Cnemidotus, Illig.) forms a distinct section having only two distinct joints in the 
antennae ; the palpi terminated by a small joint pointed at the tip, and the base of the hind legs covered by a large 
plate. Types, Dytiscus fulvus, impressus, obliquus, and many other species of very small size. 
[The family Dyticidse of English authors has been investigated by several recent authors, especially 
by Leach, in the Zool. MiscelL, vol. iii.#; Erichson, in his Genera Dyticeorum, and Kafer der 
Mark Brandenburg ; Laporte in the Etudes Entomologiques ; Say in the American Phil. Trans. 
