134 DIPLOPODA. 
median crest, and in the presence of two definite rows of tubercles on the dorsal surface external to the 
upper admedian row. 
Type, D. motzoronginis, Kenyon. 
Distribution. Mexico. 
Kenyon made a special family for the reception of this genus, but it obviously falls 
into line with the genera Pyrgodesmus, Lophodesmus, Urodesmus, and others, for which 
the group-name Pyrgodesmine had been previously proposed. 
1. Decaporodesmus motzoronginis. 
Decaporodesmus motzoranginis (sic), Kenyon, Proc. Ent. Soc. Wash. iv. p. 299 (1899) *. 
Colour brown above, lighter below. eels prominent, not decurved, with outer margins bilobed. First tergal 
plate with ten tubercles on either margin of the crest overhanging the head. Keels of second segment 
projecting forwards ; the rest projecting outwards, except at the posterior end, where they incline more 
and more backwards. Last tergal plate pointed (?), marginally 5-tuberculate. Dorsal crest consisting 
of two or three tubercles and increasing in height posteriorly. The crests converging on the 18th 
segment, and uniting on the 19th and 20th to form a median crest which projects considerably 
backwards. Between these crests and the base of the keels there are two rows of simple tubercles, the 
inner of these rows more prominent than the outer. 
Length about & millim., width ? 
Hab. Mexico, Motzorongo in Vera Cruz (Bruner !). 
Fam. PERIDONTODESMIDZ, nov. 
Antenne widely separated, the distance between them about equal to the length of their three basal segments, 
clavate, the sixth segment the longest and thickest. First tergal plate small, without keels, Segments 
2 to 19 with well-developed, nearly horizontal keels, the lateral and posterior edges of which are armed 
with strong teeth each tipped with a bristle, the median area of the segments with three rows of setiferous 
tubercles. Keels of second segment much larger than those that immediately succeed them. Pores 
normal in number, placed above the lateral border of the keels in their posterior half. Caudal process 
triangularly pointed; sternal plate with broad truncate posterior border. Sternal areas moderately 
wide. Legs with sixth segment longer than the third. Phallopods, where known, of a very special 
type and different from those of all described Polydesmoids. 
Distribution. CENTRAL AMERICA. 
Cook (‘ Brandtia,’ v. pp. 15-16, 1896) suggested that the genus Peridontodesmus 
might belong to the Xystodesmide, a family of which the characters do not appear to 
have been categorically detailed. It was established for several genera based upon 
species from tropical West Africa and South America, amongst the latter being Trachelo- 
desmus, Peters. I cannot, however, find any evidence of relationship between 
Peridontodesmus and Trachelodesmus. Rather does it appear to me possible that Peri- 
dontodesmus is allied to Cryptudesmus, of which the type, according to Cook’s selection, 
is C. olfersiz, Brandt. In the latter, according to this author (‘ Brandtia,’ p. 19, 1896), 
the terga have three rows of setiferous tubercles, the lateral and posterior margins of 
the keels are sinuato-dentate, the pores are normal and submarginal, the antenne are 
