No. I.] A NEW PERIPATUS FROM MEXICO. 3 



line also in some specimens of P. trinidadensis Sedgwick, 

 although it is so much obscured by the shrinkage of the integu- 

 ment that I should have overlooked it had I not previously 

 found it in P. eiscnii. The impressed line may be somewhat 

 narrower and fainter than it is in the Cape species {P. capensis 

 Grube and P. tnosclcyi Wood Mason ; see Sedgwick's PL XVII, 

 Fig. 10), but its presence in at least two of the American 

 species is sufficient reason for excluding it in future from the 

 diagnosis of the South African division of the genus. 



The antennae and oral papillae resemble the corresponding 

 organs of P. edwardsii. The jaws, too, resemble the jaws of 

 the Venezuelan species, except that the inner blade bears three 

 teeth before the diastema instead of two. The additional 

 tooth is a smaller second "minor" tooth. The teeth of the 

 series beyond the diastema are less numerous and blunter 

 than they are in P. edivardsii. The outer blade of the jaw in 

 P. eiscfiii bears only two teeth, like that of the other species 

 of the genus. 



The papillae and folds surrounding the mouth differ from 

 those in the same position in P. cdzuardsii. These differences 

 are best seen by comparing Sedgwick's PI. XVIII, Fig. 15, 

 with my Fig. 2. 



P. eisenii resembles the other American species in having 

 a variable number of legs. The legs in all the specimens, old 

 and young, were counted, and were found to vary from 23 to 

 29 pairs. The extremes were each represented by a single 

 specimen. Four had 26 pairs, 1 1 had 24, 17 had 25, 22 had 27, 

 and 30 had 28 pairs. The peculiar curve plotted from these 

 data has two summits as shown in the accompanying figure. 



This peculiar variation in the number of pairs of legs is not 

 due to growth, as Sedgwick has shown in other neo-tropical 

 species. The animal is born with the definitive number of legs, 

 and no further pairs are added during post-embryonic life. 

 Several of what I take to be just-born young, only 1 1 to 13 mm. 

 long, have 27 or 28 pairs of legs, whereas several larger speci- 

 mens, 20 to 28 mm. long, have only 24 or 25 pairs. 



According to Sedgwick, the greater numbers are found in 

 the females, the lesser in the males. I have been unable as 



