DESCRIPTIONS OF ttENERA AND SPECIES. 205 



serratum, is apt to bear mammilliform elevations, or 

 lumps ; one of which may form the antero -lateral, and 

 one the postero-lateral angle of the abdomen. When 

 these mammilliform processes are present, they each 

 usually bear a hair, which may be quite short, as in H. 

 rostro-serratum ; or may be longer than the whole body, 

 as in the Italian species H. flagelUf&r. The notogaster 

 may also have its hairs transformed into great leaf -like 

 scales, as in the Italian species H. phyllotrtchum, or 

 into long curved spines as in H. spiniferum, or into stiff 

 ensiform spines as in H. pulckrum. 



The Legs are usually, but not invariably, long and 

 thin ; especially the tarsus, which is sometimes as long 

 as all the other joints added together ; they often bear 

 short, stout spines, sometimes fine hairs. The tarsus is 

 terminated by a claw, which is generally long and very 

 slightly curved, without sucker or caroncle. 



The Ventral Surface. The development of the 

 chitinous epimeral skeleton varies in different species ; 

 the sternum is usually short. The external genital 

 organs are generally placed between the coxae of the 

 fourth pair of legs. The vulva is a mere longitudinal 

 slit with protecting sclerites. There are generally two 

 pairs of discs with chitinized edges, which resemble 

 suckers ; some authors identify them with the genital 

 suckers found in most other genera of the family : they, 

 however, differ considerably from the ordinary genital 

 suckers both in appearance and position ; they are not 

 even within the genital area, emerging between the 

 genital labia, as is usually the case with the genital 

 suckers of other genera, but are often quite distant 

 from the genital opening. There are not any anal 

 (copulative) suckers. 



The Immature Stages. The larvae and nymphs 

 usually resemble the adults, with the ordinary excep- 

 tions ; but hairs, spines, and scales are apt to be less 

 developed than in the adults. The hypopial stage is 

 a very important one in the lif e -history ; hypopial 

 nymphs are extremely abundant in such species as 



