THE MYRIAPODA OF NORTH AMERICA. 155 



varies exceedingly, even during life. Size is often a good distinguishing character of a 

 species, although scarcely available for the identification of an individual. 



If we consider a species as the expression of a preconceived idea, there must be, as it 

 were, a type of every species around which the individuals cluster, restrained from depart- 

 ing beyond a certain limit from the central nucleus. We can see then how there may be 

 species perfectly distinct, but the individuals of which may so approximate that there may 

 be difficulty in placing some of them. Does the mere difficulty or impossibility of placing 

 an individual necessarily invalidate the claims of the species X The moss Leucobryum 

 glaucurn, Hampe, is acknowledged by all botanists (I believe) as distinct from L. minus, 

 Hampe, the most tangible difference being that the former fruits in October, the latter in 

 May. Now I have found fruiting specimens in April, which are undoubtedly referable 

 to L. glaucurn ; but had they been found a month or two later, would any botanist have 

 hesitated in labelling them L. minus ? Indeed, one of the best American authorities told 

 me, that had I so found the specimen, he would have pronounced it to be L. minus, as it 

 would not have been possible to have known that the capsules were those of the previous 

 year. 



In the other genera of the Scolopendridse the specific characters are pretty much the 

 same as in the true Scolopendra. But some characters specific in the latter, elsewhere 

 become generic subcharacters. 



Subfam. I. SCOLOPENDRLNL/E, Newport* 

 " Spiracula valvularia in paribus 9." 

 Spiracles valvular in 9 pairs. 



Gen. 1. SCOLOPENDRA, Linn. 



Segmentum cephalicum imbricatum. Oculi stemmatosi, utrinque 4. Antennae attenuate. Pedum paria 21. 



Cephalic segment imbricate. Ocelli stemmatous, 4 on each side. Antenna; attenuate. Pairs of feet 21. 



S. HEROS. 



S testacea ; segmento cephalico subovato, minute punctato ; antennis 25 articulatis ; dente mandibulari pro- 

 ducto, gracile ; dentibus labialibus 8 — 10, duobus intimis utrinque plerumque coadunatis ; pedibus plerumque 

 luteolis; paris postremi articulo basali, intus 5 — 7 spinis,f subtus 7 — 10 spinis in scrie triplici dispositis, processu 

 angulari 3 — 10 spinis; appendicibus analibus lateralibus elongatis, minute profunde punctafcis, spini*»apicalibus 

 utrinque 5 — 7 et altera marginale armatis. 



* Linn. Trans., vol. xix, p. 377. 



f When giving the spines on the inner edge of a leg, I do not (as some do) include those on the terminal 

 angular process; these arc afterwards given separately. 



