THE GENERA AND SPECIES OF SYMPHYLA. 13 



rather superfluous in the descriptions of the species. The 

 two scuta present excellent specific characters, being not 

 quite similar in any two species, and differing not only as to 

 shape and distance of the triangular plates, but also in the 

 number of marginal setae on these plates, in the length of 

 the antero-lateral seta, etc., while the individual variation 

 seems to be slight in all respects. 



In Scutigerella the scuta present several excellent cha- 

 racters, but not as many as in the other genus. The shape 

 of the posterior margin of all the scuta, the last one excepted, 

 of tlie same specimen is rather similar in the main features; 

 the last scutum differs in the whole order essentially from 

 the others in shape and endowment with setae. I have found 

 the second and the penultimate scuta to be more different 

 from each other than the intermediate ones, and these two 

 scuta are therefore described in all species. The marginal 

 seta3 of the scuta present good characters, but their length 

 shows some individual variation. A pair of antero-lateral 

 setae are often especially elongate on the anterior scuta or on 

 nearly all scuta ; these setse are always inserted on the most 

 lateral point of the scutum (consequently where this is 

 broadest) ; on the anterior scuta this point is situated much 

 in front of the middle, on the posterior scuta behind the 

 middle. When these sette are especially elongate they are at 

 least on the anterior scuta and sometimes also on the 

 posterior scuta directed outwards and less or more forwards. 

 Furthermoi'e, the longest pair of lateral setse are generally 

 of importance, and some other small features are mentioned 

 in the descriptions of the species. The last scutum presents 

 a very curious structure in two closely allied species, Scut, 

 immaculata (Newp.) and Scut, armata, n. sp. : an oblong 

 median area at the hind margin is so deeply impressed or 

 invaginated that a cavity is formed, the anterior part of 

 which is overlapped by the protruding dorsal wall ; around 

 this cavity (PI. 1, fig. 1 c) a belt of the interior tissue shows 

 a peculiar aspect, indicating the existence of an organ which 

 probably is a gland, but a special investigation of the 



