COLKOPTERA. 409 



their origin to the extremity ; the last joint of the labial palpi is 

 simply obtuse at the end and unemarginate. Such is 



Dytiscus, proper. 



"Where all the tarsi are composed of five very distinct joints, of 

 which the throe 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 sulcated and carinated 

 in the female. From the department of Vosges in the north 

 of Europe and from Germany. 



D. marginalia, L. ; Panz. lb. 3. About a fourth smaller ; a 

 yellowish border all round the tliorax, 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. 



Fabricius says that if laid on its back, it soon regains its 

 natural position by jumping. 



Espcr preserved a D. marginalis for three years and a half, in 

 perfect health, in a 1 irge 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 pact of the bcdy 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. ; Roas., Insect., II, Aquat., Class I,ii. Nar- 

 rower, or more oval and more depressed than the preceding 

 ones; exterior margin of the thorax and elvtra yellowish; the 

 latter finely striated in the female. Environs of Paris, and Ger- 

 many. 



D. serricornis, Payk., Nov. Acad. So. Stock., XX, i, 3. Pte- 

 markable for the anomalous form of the antennse 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 ha\e also induced him to esta- 

 blish some others, such as Hydaticus (Z). Ilyhneri, transversalis, stagnuUs, i-vilta- 

 tus) : AciLius {D. SMlcaius) : and Trogus (D. lateralis). The last is the only one 

 that can be retained on account of some other characters. The tibife 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 rM D. sulcatus, Fab.; Clair., Entom. Helv., II, 

 XX ; — D, costalis, Oliv, Col. Ill, 40, 1, 7 ; — D. punctatus, lb. I, 6, b and I, e ; — D. 



