52 



[July. 



ON THE BRITISH QYllimBM. 

 BY D. SHARP, M.B. 



The GyrinidcB must be considered as one of the most peculiar and 

 interesting of all the groups of beetles which are found in this country. 

 The family, though it contains very few genera and species, is among 

 the most sharply defined ; indeed, though it possesses points of resem- 

 blance on the one hand with the Dytiscida, and on the other with the 

 Parnid(je, it is so distinct as to forbid the idea of its being descended 

 (in a Darwinian sense) from either of them, unless we suppose that an 

 extremely free disappearance of connecting links, of which we can now 

 find no trace, has taken place. It is also interesting to notice that a 

 genus of Carabidcd, Adelotopus of Hope, more resembles the Gyrinidcs in 

 general appearance than do any insects of either of the two families to 

 which it is allied : not only is the facies of Adelotopus that of Gyrinus, 

 but both possess two separate eyes on each side the head, a peculiarity 

 of structure almost, I believe, without parallel in the rest of the 

 Coleoptera ; the antennae, too, of Adelotopus are very short and com- 

 pressed, so as to show a great resemblance to those of Gyrinus ; indeed 

 the similarities hetsveQn Adelotopus and the Gyrinida appear to be 

 exactly of the character that has been called mimicry ; and it is also 

 worthy of note that the GyrinidcB, or the insects mimicked, exhale a 

 peculiar nasty-smelling fluid when handled. As the Gyrinidce inhabit 

 exclusively the surface of the water, and Adelotopus lives "Under the 

 bark of trees, no theory of protection founded on natural selection can 

 account, I should imagine, for this remarkable reproduction of peculiar 

 characters in very distinct groups. 



Thomson (Skandinaviens Coleoptera, Vol. II. ) places the Gyrimidce 

 •along with Parnus, Keterocerus, and others in a group which he calls 

 Amphihii; but they are now generally considered a distinct family, and, 

 along with the Dytiscidce, form the group called Hydradepliaga. The 

 characters by which the GyrinidcB are distinguished from the other 

 Hydradepliaga are so very peculiar, that, though my object at present 

 is only to call attention to the characters of our British species, it is 

 impossible to pass over these interesting points without some short 

 notice of them. 



1st. The structure of the trophi is different from what holds in any of 

 the Dytiscidcdi though not very peculiarly or decidedly. 



2nd. The Gyrinidce possess a pair of eyes on each side of the head, and 

 these are placed so that the upper ones enable the insect to see 



