544 HEMIPTERA CHAP. 



more or less modified for the reception of the tibia when closed on it : mostly 

 aquatic forms, 2. Pagiopoda. 



Division 1. TROCHALOPODA. 



This division includes the majority of the families of Heteroptera viz. 

 the whole of the terrestrial families except Saldidae, and it also includes 

 Nepidae, a family of water-bugs. 



Division 2. PAGIOPODA. 



This includes the six purely aquatic families of Heteroptera, except 

 Nepidae, which appear to have very little connection with the other aquatic 

 bugs. The only terrestrial Insects included in the family are the Saldidae ; 

 in these the femora are not modified as they are in the aquatic forms. 

 Hemiptera that live on the surface of water, not in the water, are classed 

 with the terrestrial species. With these exceptions this arrangement agrees 

 with that of Gymnocerata and Cryptocerata as usually adopted, 1 and 

 therefore followed in the following pages. Schiodte's characters, moreover, 

 do not divide his two divisions at all sharply. 



Sub-Order II. HOMOPTERA. 



Tarsi usually three-jointed . . Series Trimera. 



two-jointed . ,, Dimera. 



,, of one joint . . ,, Monomera. 



The classification of Homoptera is in a most unsatisfactory state ; 2 no two 

 authors are agreed as to the families to be adopted in the series Trimera. 

 We have recognised only five viz. Cicadidae, Fulgoridae, Membracidae, 

 Cercopidae, and Jassidae. The Dimera consists of Psyllidae, Aphidae, 

 Aleurodidae ; and the Monomera of Coccidae only. It is usual to associate the 

 Dimera and Monomera together under the name of either Phytophthires or 

 Sternorhyncha, but no satisfactory definition can be given of these larger 

 groups, though it seems probable that the families of which they are com- 

 posed are natural and distinct. 



Sub-Order I. HETEROPTERA. 



Series 1. Gymnocerata. 



The majority of the terrestrial families of Heteroptera form 

 the series Gymnocerata, in which the antennae are conspicuous, 

 and can be moved about freely in front of the head, while in 



1 A table of the families is given by Ashniead, but does not work out quite 

 satisfactorily, Entom. Americana, iv. 1888, p. 65 ; a brief table of the characters 

 of the British families is given by Saunders, Hemiptera-Heteroptera of the, British 

 Islands, 1892, p. 12. 



! Those who wish to see tables of the families are referred to Ashniead, loc. 

 cit. ; to Pascoe, Ann. Nat. Hist. (5) ix. 1882, p. 424 ; to Stal's Hemiptera Afri- 

 cana, vol. iv. 1866 ; and for the families found in Britain to Edwards, Hemiptera- 

 Hbmoptera of the British Islands. For a discussion in Danish on the value of the 

 characters used, cf. Hansen, Ent. Tidskr. xi. 1890, pp. 19-76. 



