COLEOPTERA. DYTICIDiE. 93 



informed by Mr. Davis. The species are comparatively numerous, 

 but they require a more minute investigation into their specific cha- 

 racters than has hitherto been given to them. The genera are for 

 the most part established upon the form of the thorax, the majority 

 being considered by late French authors as sections only of the genus 

 Bembidium. 



The exotic genera do not offer material for particular observation. 



The second stirps of the predaceous beetles (Pentamera Adephaga) 

 comprises those species which are aquatic in their various states, and are 

 the HYDRADEPHAG A o^ BlacLeaij (Hydrocanthari Latreille), con- 

 sisting of the Linnaean genera Dytiscus (Dyticus) andGyrinus, in which 

 the legs are formed for swimming, the two posterior pairs being flattened 

 and fringed with hairs (^Jig' 5. 7.), the hind pair being placed at a con- 

 siderable distance from the others, whereby a much greater impulse 

 is given to the animal in its motions through the dense element of 

 which it is an inhabitant. The body is oval, and generally depressed ; 

 the head broad and immersed in the prothoracic cavity ; the mandibles 

 short and strong, being nearly concealed by the upper lip ; the eyes 

 but slightly prominent ; the inner lobe of the maxillas curved from 

 the base, and not articulated at the tip. The thorax broader than 

 long, and the tarsal claws often unequal in size. 



These insects swim with agility, occasionally rising to the surface 

 for respiration, the feet at such times being held still and the body 

 ascending, being specifically lighter than the water : in this situ- 

 ation they rest obliquely, the extremity of the body being pro- 

 truded out of the water, whereby the air is enabled to enter the large 

 space beneath the elytra and reach the spiracles along the sides of the 

 back. When captured they emit an extremely disagreeable odour, 

 arising from a fluid which they discharge; a white milky liquid is also 

 of"ten emitted. They occasionally fly during the night, at which times 

 they are often attracted by a lighted candle. The larva? are long and 

 narrow; those of the (jyrinidae are depressed, and those of the Dyticida^ 

 convex, being composed of eleven segments, exclusive of the head, 

 which is large and armed with two strong sickle-shaped jaws, a pair 

 of short antenn;c, four palpi, and six minute eyes on each side of the 

 head ; the first segment is the largest, and corresponds with the pro- 

 thorax of the perfect insect, and almost similar in texture to the re- 



