128 DIPLOPODA. 
in size and shape between the keels of the fourth and sixth. The latter narrow and acutely angular with 
convex inferior edge. The five or six succeeding keels like them ; but towards the posterior end of the 
body the keels become gradually broader and contiguous, the anterior angle becoming gradually more and 
more convex and the posterior more and more pointed and acute. The posterior border of the sixteenth 
inclined slightly backwards; that of the nineteenth forming an obtuse angle with the posterior border of 
the segment. Dorsally the segments are markedly depressed in front. Anal tergal plate moderately 
large, lightly compressed, with projecting inferior (posterior) border, hardly twice as wide as high; sternal 
plate with convex, bitubercular posterior margin. Legs with second segment much more than half the 
length of the third and longer than the fourth and fifth. 
In the male the legs of the first pair are modified, the femur being stout and strongly convexly arched above, 
with a conspicuous dentiform tubercle near the base below. Sterna of fifth and sixth segments quite 
narrow ; but the second segment of the legs long and curved slightly backwards to make room for the phallo- 
pods. Socket of phallopods very large and wide, its margin not noticeably raised; sternal area between 
the posterior legs of the seventh segment very narrow, scarcely exceeding the width of the basal segments 
of the legs. Phallopods widely separated by a submembranous area; basal segment stout, vertical, convex 
externally, concave internally for the lodgment of the distal segment, which arises on their inner aspect, 
and from the inferior view at least appear to be two-jointed ; the proximal portion stout and short, with 
a posterior and an anterior tuft of bristles, the latter tuft overlapping the proximal end of the distal 
portion ; the latter elongate, strongly convex, and distally curved upwards and outwards, with a hair- 
tipped excrescence at the base on the outer side and a fringe of hairs on the apex; the hollow of this is 
occupied by a less chitinised piece, which also ends distinctly in a pointed process, so that the segment 
in question is apically bifid. 
Length 8 millim., width about 3. 
Hab. Guatemats, Volcan de Agua (Stoll). 
2. Cylionus gracilis. 
Spheriodesmus gracilis, Humb. & Sauss. Rev. et Mag. Zool. 1869, p. 149°; Miss. Sci. Mex., Myr. 
p. 22, t. 1. figg. 2-2/1 (1872)*; Attems, Denk. Akad. Wien, Ixviii. p. 391 (1900)’. 
Cylionus gracilis, Cook, Pr. U.S. Nat. Mus. xxi. p. 463 (1898) *. 
Apart from the original describers, no one seems to have seen examples of this species. It is not easy to 
extract from the description and figures any well-marked specific features to separate it from C. constrictus, 
except those presented by the structure of the phallopods, which are totally different in the two forms. 
It may be added, however, that the third tergal plate does not appear to be so long and wide laterally in 
C. gracilis as in C. constrictus. Judging from the figure of C. graczlis, the phallopods are rather less 
widely separated, and the distal segment arises much less markedly from the inner aspect of the proximal 
than in C. constrictus. The proximal portion of the distal segment also is much longer and bears two 
incurved processes, the inferior forming a simple pointed flagelliform hook, and the superior an equally 
strongly incurved apically bifid process. Other sexual characters are not recorded; but about the specific 
distinctness of the two forms there can be no doubt whatever. 
Length 11 millim., width 2:5, 
Hab. Mexico, Moyoapan in the Eastern Cordillera !~4. 
COLOBODESMUS. 
Colobodesmus, Broélemaun, Ann. Soc. Ent. Fr. Ixxiv. p. 847 (1905). 
The name Colobodesmus was proposed by Brélemann for a species of this group 
apparently resembling Spheriodesmus in external features, but separable from all the 
members of that genus in which the phallopods had been described by the structure 
