ORDER COLEOPTERA. 247 



with avidity, and suck the blood out in the most complete 

 manner. It is capable of fasting for four weeks at least. 

 It kills the brown hydrophilus, though as big again as 

 itself, by piercing it between the head and the corslet, the 

 only part of the body which is without defence. According 

 to Esper it is sensible to the changes of the atmosphere, and 

 indicates them by the height to which it rises in the bottle. 



D. Roeselli^ Fab. Roes. In. II. Aquat. Class. I. ii. 

 More narrow, or more oval, and more depressed than the 

 preceding. The external edge of the corslet and wing-cases 

 is yellowish. These cases are very finely striated in the fe- 

 male. Found in the neighbourhood of Paris, and in Ger- 

 many. 



D. Serricornis, Payk. Nov. Sect. Acad. Scient. Stockh. 

 XX., 1. 3. Very singular from the irregular form of the 

 antennae in the male, of which the four last articulations form 

 a compressed mass, and denticulated like a saw.* 



CoLYMBETES, Clairv. 



In which all the tarsi have also five articulations very dis- 

 tinct, but the anterior four have, in the males, their first 

 three articulations equally dilated, and form together only a 



* Dr. Leach has founded on this character his genus, Agarus — (Zool. 

 Misc. III. pag. 69, and 72.) Some slight differences in the form and 

 relative proportions of the articulations of the external maxillary palpi 

 have also determined him to establish some others, such as those of 

 Hydaticus {D, Hyhner'i, transversalis, stagnalis 4-vittatus) of AciLias (Z>. 

 Sulcatus), and of Trogus (D. lateralis). The last alone may be preserved 

 in consequence of some other characters. The hinder feet have the legs 

 short, very broad, and their tarsi are terminated only by a single crotchet. 

 To the species described above, add, D. Sulcatus, Fab. Clairv. Entom. 

 Helv. II. XX ; D Castalis, Oliv. Col. III. 40. 1. 7j D. punctatus, ibid. 

 1. 6. 1. and 1. e.; D. aciculatus, ibid. Ill 50; D. Icevigatus, ibid. 25; 

 D. tripunctatus, ibid. 24; Ruficollis, ibid. ii. 20; Z>. vittatis, ibid. 1. 5; 

 D. griseus, ibid. ii. 12 ; Z>. stlcticus, ibid- ii. 2; D. circuniflcxus, F. 



