COLEOPTERA. 503 



Tlie aquatic, carnivorous, pcntamcrous Coleoptcra, form a tliinl tribe, tliat uf 

 The IIydrocantham, or Swimmers. 



Tlieir feet are formed for swimmina;, the four posterior being compressed and ciliated, or in the form 

 of plates, and the two hind ones are far apart from the otliers. The mandibles are nearh' covered [by 

 the upper lip], the body is always oval, with the eyes slightly prominent, and the thorax much broader 

 than long : the hoolc which terminates the niaxillrc is curved from the base ; the ungues are often unequal. 



These insects compose the genera Dytiscus and Gi/rhms of Geoffroy. They pass the first and the 

 last state of their existence in fresh water, such as lakes, pools, and ditches. They swim well, and 

 rise to the surface of the water from time to time to respire, ascending easily by holding their feet 

 still and suifering themselves to float. The body being turned upside down, they slightly elevate the 

 tip of the body above the surface of the water, raising the extremity of the elytra or bending down the 

 abdomen, so that the air introduces itself into the spiracles, which they cover, and from thence into 

 the tracheic. They are very voracious, and feed upon small animals which, like themselves, ordinarily 

 reside in the water, which the Hydrocanthari only leave at the approach of or during the night. AVhen 

 taken out of the water tliey ennt a very disagreeable odour. Tliey are sometimes attracted by the 

 light into the interior of houses. Their larvffi have the body long and narrow, composed of twelve 

 segments, of winch the first is largest, with the head strong, and armed with two i)owcrful mandibles, 

 ■which are curved into an arch and pierced near the tips ; they have also short antenna?, i>alpi, and six 

 simple eyelets close together on each side of the head. They have six feet of moderate length, often 

 fringed -iiith hairs, and tcrnnnated by two small books. They are active, carnivorous, and respire 

 cither Ijy the anus, or by a kind of swimmerets resembling gills. They quit the water in order to 

 inidergo their metamorphosis into pupa3. 



This tribe is composed of two principal genera. 



Dytiscup, Geoff.,* — 

 Which have thread-like antenna; longer than the head, two eyes, the fore legs shorter than the fol- 

 lowing, ami tlio posterior often tcrnunatcd by a compressed tarsus finishing in a }ioint. They s^iui 

 ■with great quickness by the assistance of their feet, fringed with long hairs, especially the posterior 

 l)air. They dart forward upon other insects, aquatic worms, &c. In the majority of the males the 

 four anterior tarsi have the three basal joints dilated and spongj' beneath ; those of the first pair arc espe- 

 cially remarkable in the large species, in which these three joints form a broad plate, the under surface of 

 ■which is covered with small bodies, some of them like v^'arts and others like small suckers. Some females 

 are distinguished by their elytra being furrowed. The larvae have the body composed of eleven or twelve 

 segments covered by scaly plates ; they are long, swollen in the middle, and slenderer at each end, especially 

 when the terminal segments form an elongated cone fringed at the sides with floating hairs, with which 

 the animal beats the water and thus propels the body forwards, which is ordinarily terminated by two 

 conical bearded anil moveable filaments, between ■which are two small cylindrical bodies pierced with 

 a ^uttcr, at tlie extremitv which are aerial channels, to which arc attached two trachea? ; moreover, the 

 sides of the body are provided with spiracles : the bead is large, oval, attached to the thorax by a neck 

 with strongly-armed nnindiblcs, beneath the extremity of which De Gecr observed a longitudinal slit, so 

 tliat these organs resemble the ijiandibles of the larva; of the Myrmeleons, or Ant-hons, and serve them 

 for suckers : the mouth offers besides a pair of maxillae and a Up with palpi : each of the three first 

 segments supports a pair of moderately long legs, of which the tibia and tarsus are fringed with hairs, 

 which are serviceable in swimming ; the first segment is the broadest or longest, and defended beneath, 

 as well as above, by a scaly plate. 



Tliese larva; suspend themselves at the surface of the water by means of two appendages at the sides 

 of the tail, which they keep dry by raising them above the smface. When they wish to change their 

 place suddenly, they give their body a quick and vermicular movement, beating the water with the 

 tail. They especially feed upon the larva: of Dragon-flies, Gnats, Tipula;, Aselli, &c. When the period 

 of llicir transformation has aiTived, they quit the water and bury themselves under the earth of the ad- 

 jacent banks, keeping, however, in very damp situations, where they form an oval cavity in which they 



• [r.iLtrcllIc is incorrect in giving GcolTrr,;' ns Uic author of 0,c j cnnlrarv, corrected it to Dyticus, bcini,' derived frojii tlic Orcelt 

 □ am.- nytisccs it i^^vinj,' been ]>ropo5cd liy l.innicns. GeofFroy, on the ] DctUihm, nrinatnrius.] 



