( Isv) 



has the spines mostly along the enter edge, where the_v become sometimes very 

 stout and long {Proi<erpiiu(s ; Arctonotus). The spurs of the tibiae are organs 

 of much importance in the classiticatiou of Moths, their number and length 

 being constantly made use of in systematic works in the definition of genera. 



The epiphysis or spur of the foretibia,* which we consider homologous with 

 a proximal spur of the hiudtibia, varies in length and jwsition in the Sphiiigidae. 

 It is never absent, as in C/udcosiidae for instance. The most remarkable form 

 is that in which the fringe is obliterated {Ceridia). The midtibia has one pair 

 of slender si>urs, which end in a naked point as a rule and are proximally 

 generally cylindrical. They are sometimes of the same length, but as a rule the 

 outer or anterior one is shorter. A ipiite exceptional development found among 

 the species of the American Choerocampiue genus Xijlophanes leads to the outer 

 spur being the longer one of the two. The variation in length is considerable, 

 the longer spur being sometimes as long as the tibia and frequently barely 

 longer than tiie tibia is broad. There are on the spurs generally some long 

 hairs, which develop often into sj)ines. The spinosity of the spurs is a feature 

 often met with in species witii spinose tibiae, and is, like the latter, a sign of 

 reduction or weakness. 



In some cases we iind a series of stiff scales along the side towards 

 tlie tarsus, resembling a serrated crest (Mar roff loss tan) ; while there occurs a 

 conspicuous comli of bristles on the shorter spur in Nephele and Centroctena 

 (PI. LXIV. f 8). The comb of Nephcle and Centroctena has most likely the same 

 function as the comb of the tarsus, as described below. The midtibial spurs are 

 never absent from Sjdiinyidae. 



The hindtibia jiossesses normally two pairs of spurs, one terminal, and 

 the other more jn'oximal, situated sometimes in or near the middle of tiie tibia, 

 sometimes near tlie terminal spurs. The shape and structure of the iiindtibial 

 spurs resemble tliose of the midtiliia ; they are longer on an average, the longer 

 apical Iiindtibial one being never shorter than the longer midtibial one, but 

 very often surpassing it in length. They are less often spinose ; the inner one is 

 never shorter than the outer one of the same pair, and the comb or crest found 

 in JS'epliele, etc., is less strongly developed. The proximal pair disappears very 

 often. The gradation from a tibia with long proximal spurs to one without a 

 trace of them is complete, tiiere being many species with very short spurs, and 

 one {Paium porphyria) in which there are two very short proximal sjjurs or 

 only one or no spur. Here we have a case where there can be no doubt about 

 the direction of the line of develojtment. The absence or reduction of the 

 j)roximal pair of sjiurs is a specialisation, the species thus characterised repre- 

 senting a younger stage of development than those in which the proximal spurs 

 are long. And therefore we can safely conclude that also in the case of the 

 midtibial spurs shortness is a sign of reduction. .Short spurs are seldom found 

 outside the Acherontiinae and AmbuUcinae, and the cases where the proximal 

 pair of the hindtibia is absent are nearly all confined to those two subfamilies, 



• Kathreiner, llludr. Zcitxckr. Entom. iv. p. 113. Hil. Plate (1899). 



