145 



desired. The passage from the Hydradephaga to 

 the Philhydrida has been pointed out by Mr. 

 Stephens, by means of the sub-aquatic families of 

 Heterocerus and Parnus. Would it not be a more 

 natural arrangement to keep together all the true 

 Aquatics, as Linneus did at first, and then pass to 

 the terrestrial groups, by families which may justly 

 be considered amphibious in their habits? At present 

 we are imperfectly acquainted with these groups, 

 and know little of their larvse, and until that period 

 arrives, the natural distribution of these families 

 must still remain in doubt and confusion. The 

 following table is an outline of the genera compos- 

 ing the Gyrinidse. 



Gyrinus, Linneus. 

 Gyrinid^, Leach. 

 Gyrinoidea, Hope, 



Genera. 



Country. 



Typical Species. 



1. Gyrinus, Linneus 



England 



G. Natator, Linn. 



f Enhydrus, Laporte 

 2. < Cyclinus, Kirby 

 (, Cy clous, Eschscholtz 



N. America 



G. Australis, Fab. 



3. Porrorhynchus, Lap. 



Java 



P. Marginatus, Laporte. 



4. Dineutes, MacLeay 



East Indies 



D. Politus, MacLeay. 



i Gyretes, Brulle 

 o. < 



( Cybister, Esch. 



East Indies 



G. iEneus, Brulle. 



i Potamobius, Leach 

 ' ( OrectocheiluS, Mul. 



England 

 England 



Pot. Modeerii, Marsham. 

 G. Villosus, Fab. 



