On Aquatic Carnivorous Coleoptera or Dytiscidce. 959 



the antenna in Copelatus pulitus ; the display of a file of fine rugte in some of the 

 species of Agabus (group 8) on the tliird venti'al segment ; and the existence of a 

 similar structure on the edge of the second ventral segment in numerous species of 

 Colym betes, and in a few PJianti. The form of the eoxal processes in Agabinus is 

 very peculiar, reminding one somewhat of Noterus. Hydrotrupes and Coptotomus 

 show peculiar labial palpi. A.nd in Platambus we have a remarkable increase in 

 the posterior portion of the epipleur*, which however is approximated by certain 

 Agabi. In Matus we have a conspicuous sulcation of the presternum which is repro- 

 duced in Spencerhydrus, a genus of Cybistrini. While in several genera (A.gametrus, 

 Metronectes, and others) we have the very exceptional occurrence of a complete 

 efFacement of the coxal lines. Colymbetes reticulatus, (Laucetes) shows a difference 

 in the colour of the ventral segments of the two sexes, similar to what exists in 

 certain species of Bidessus and Coelambus, in the Hydroporides. 



The interesting Madeiran species of Meladema, (Dytiscus lanio) makes an approach 

 to the genus Dytiscus in several respects, and it has the suture on the front of the 

 head distinct as is the case in that genus, and the clypeus is coloured yellow as in 

 that genus, while the two pale marks on its vertex seem to indicate the manner in 

 which the angular mark on the front of the head of Dytiscus has been developed 

 from the two pale spots so common in the Colymbetides. 



As regards geographical distribution little can be said, except that the great 

 majority of Colymbetides are inhabitants of the northern parts of the Eastern and 

 Western Hemispheres, but one large genus (Copelatus) is on the contrary chiefly 

 tropical. 



TIL 4.— Tribe HYDATICIDES. {Vide p. 647.) 



This tertiary aggregate consists of about one hundred species arranged in five 

 primary aggregates, plus three isolated species ; and in the second synthesis these 

 are reduced to two aggregates, plus an isolated primary aggregate. 



They are all insects of moderately large size — one-third of an inch to two-thirds 

 of an inch in length : the colour of the surface is generally variegate. 



The head is short, the eyes are large, the insertion of the antenna is but little 

 protected by the side of the front, and this does not infringe on the circular outline 

 of the eye ; the frontal suture can be detected only at each side ; the antenna are 

 elongate and slender but to a variable degree. The hind coxae are large, and the 

 wing of the metasternum has always a slender sub-parallel deflexed band as its 

 terminal portion ; this band is however very variable in its length according to the 

 amount of forward extension of the hind coxa. 



The coxal lines are always short, (sometimes quite obliterated) and in front they 

 are very far indeed from attaining the front border of the coxa ; the coxal lobes are 

 never elongate and are always broad in proportion to their length, and when the 



