no. 1831. NEW TROPICAL MILLIPEDS—COOK. 467 



family Peridontodesmidae. Scytonotus is a specialized type that cer- 

 tainly stands well apart from the now rather numerous genera of 

 true Polydesmidae in the structure and sculpture of the segments, as 

 well as in the numerous and highly specialized secondary sexual 

 characters. This has been recognized by Attems in his System der 

 Polydesmiden, where our North American Scytonotus is associated 

 with members of the South American family Trachelodesmidae, 

 though the lack of any true relationship is admitted. The structure 

 of the gonopods of Scytonotus is also peculiar in that the basal joint 

 is unusually large and somewhat hollowed out to accommodate the 

 second joint. Though the specialization is not carried to any such 

 extent as in the Stylodesmoid series, the analogy is suggestive. In 

 Peridontodesmus , according to Pocock, the basal joints of the gono- 

 pods are fused together, a unique condition, as far as known, in the 

 entire order. 



A NEW SOUTH AMERICAN GENUS RELATED TO CRYPTODESMUS 

 AND PERIDONTODESMUS. 



The relations between Peridontodesmus and Cryptodesmus appear 

 to be very close, both in the characters of the segments and in the 

 more significant features of the structure of the gonopods. A 

 Brazilian species described by Attems as Cryptodesmus pusillus, 

 though not as similar to C. olfersii as its author supposed, is at least 

 to be considered as a member of a related genus. A comparison of 

 Attems's description and figures of Cryptodesmus pusillus with notes 

 and drawings made from the type-specimen of C. olfersii shows 

 several important discrepancies, though not such as to destroy the 

 probability of family relationship with Cryptodesmus. 



The body of C. pusillus is much smaller and more slender, seven 

 times as long as wide (7 mm. by 1 mm.), instead of about four times 

 (11 mm. by 2.5 mm.), in C. olfersii. The segments appear to be 

 relatively longer and narrower than those of C. olfersii and the body 

 is said to be broader in front, while that of C. olfersii is somewhat 

 narrowed, with the first segment not as wide as the second. 



The antennae of C. olfersii are distinctly clavate. Those of C. 

 pusillus are large and robust, but the terminal joints are not strongly 

 thickened. 



First segment of C. pusiUus is much more expanded than in C. 

 olfersii, semicircular in shape, two-thirds as long as broad; that of 

 C. olfersii transversely elliptic, less than half as long as broad. Ante- 

 rior margin even in both species, bordered in C. olfersii by a simple 

 row of flattish granules; smooth in C. pusillus, with twenty yellow 

 lobes of the inner tissues showing through the transparent chit in. 



Carinas of C. pusillus very angular and with the posterior corners 

 produced; those of C. olfersii narrowed and rounded. The delicate, 



