COLEOPTERA. 
409 
their orig'in to the extremity ; the last joint of the labial palpi is 
simply obtuse at the end and unemarginate. Such is 
Dytiscus, proper. 
Wliere all the tarsi are composed of five very distinct joints, of 
which the three first of the two anterior ones are very wide, forming, 
collectively, a palette, either oval and transverse, or orbicular. 
D. latissimus, L. ; Panz. Faun. Insect. Germ. LXXXVI, 1. 
About an inch and a half long, and easily distinguished by the 
compressed and trenchant dilatation of the exterior margin of 
the elytra, the border of which is yellowish ; thorax margined 
all round with the same colour ; elytra sidcated and carinated 
in the female. From the department of Vosges in the north 
of Europe and from Germany. 
D. marginnlis, h. •, Panz. Ib. 3. About a fourth smaller ; a 
yellowish border all round the thorax, and a line of the same 
colour on the exterior and non- dilated margin of the elytra; 
those of the female sulcated from their base to about two-thirds 
of their length. 
Fahricius says that if laid on its back, it soon regains its 
natural position by jumping. 
Esper preserved a D. marginalis for three years and a half, in 
perfect health, in a large glass jar. Every week, and sometimes 
oftener, he threw into the vessel a piece of raw beef about the 
size of a filbert, on which it darted with great avidity, and then 
completely exhausted its blood by suction. It can go without 
food for at least four weeks. It kills the Hydrophilus piceus. 
although double its own size, by piercing it between the head 
and thorax, the only part of the body that is unarmed. Accord- 
ing to Esper, it is affected by atmospheric changes, and indicates 
them by the height at which it remains in the jar. 
D. Rceselii, Fab.; Roes., Insect., II, Aquat., Class I,ii. Nar- 
rower, or more oval and more depressed than the preceding 
ones ; exterior margin of the thorax and elytra yellowish ; the 
latter finely striated in the female. Environs of Paris, and Ger- 
many. 
D. serricornis, Payk., Nov. Acad. Sc. Stock., XX, i, 3. Re- 
markable for the anomalous form of the antennae of the male, 
the four last joints of which form a compressed and serrated 
mass *. 
* Doctor Leach has established his genus Agabus— Zool. Miscel. Ill, p. 69 and 
and 72 — on this character. Certain slight differences in the form and relative pro- 
portions of the joints of the exterior maxillary palpi have also induced him to esta- 
blish some others, such as Hydaticus (^1). Hybneri, fransrersalis, siagnuUs, i-t Hia- 
tus) : Acibius {D. sulcatus) : and Trogus (D. lulerulis). The last is the only one 
that can be retained on account of some other characters. The tibiae of the pos- 
terior legs are short and very wide, and the tarsi are only terminated by a single 
hook. _ 
To the species above quoted add D. sulcalus, Fab. ; Clair., Entom. Helv., 11, 
XX D. costalis, Oliv. Col. Ill, 40, 1, 7 -—JJ. punciatus, Ib. I, 6, b and I, e L». 
