THE GENERA AND SPECIES OF SYMPHYLA. 9 



necessary to give the exact proportion between the length 

 and breadth in the various species, but only an estimate. 

 The length of one pair of lateral setse as compared with the 

 breadth of the proximal joints of the antennae is a character 

 in Scutigerella. It is well known that internal linear thicken- 

 ings of the dorsal integument have been observed in European 

 species; the thickening in the median line I name the central 

 rod; from the anterior and posterior ends of this a pair of 

 branches originate. The major part of this structure is much 

 more easily seen in Scolopendrella than in the other genus, 

 audit presents a few characters used in the descriptions below. 

 The eye-spots have been omitted as nearly valueless. 



c. Antennae. — Latzel especially has pointed out with his 

 usual accuracy that in the three species known to him the 

 number of joints varies very much in specimens of each 

 species, and above all in Scut, immaculata, in which he has 

 found from eighteen to fifty-five joints. The degree of varia- 

 tion is, on the whole, considerably larger in Scutigerella than 

 in Scolopendrella. Notwithstanding this, the number of joints 

 is not quite worthless, as it is considerably higher in some 

 species than in others. The shape of the joints is generally 

 without any significance, as it in reality is rather uniform in 

 nearly all species of the same genus, and besides presents too 

 much difference according to the degree of contraction of the 

 antennae. Sometimes this contraction is so considerable that 

 the distal part of manj' joints is concave instead of conically 

 truncate, and in this case the antennas show a very anomalous 

 appearance, the joints being only half as long as usual, but 

 considerably thicker than in their normal state, much resem- 

 bling cups arranged in a pile. Only in two species, Scut, 

 crassicornis and Scut, pauperata, the subproximal part 

 of the antennae has the joints really thickened in proportion to 

 the rest (PL 4, fig. 4 a) . Each joint, the terminal one excepted, 

 has always a whorl of stiff setffi on the thickest part ; the sette 

 in this whorl, which I name the central one, differ some- 

 what in length in the different species, and in Scut, crassi- 

 cornis and S. pauperata the setoe on the inner (anterior) 



