186 DIPLOPODA. 
forming a sheath for the principal branch or seminal stile; tracheal rods very leng, slender, and 
cylindrical. Socket or cavity of phallopods small, irregularly, transversely elliptical. 
Type, Z. cwruleus. 
Distribution. Mexico. 
In the shape of the anal sternal plate, the small size and structure of its phallopods, 
and in the small size of the cavity into which they are partially at all events retractile, 
this new genus shows marked resemblance to the two species described above as 
Pammicrophallus ornatus and P. pictus. Generic differences between them subsist, 
however, in the large size of the keels, which are depressed and overlap throughout 
the Jength of the body, in the deeply angular and bitubercular posterior margins of 
the sternal areas, and in the comparative shortness of the sixth segment and the 
greater length of the fourth and fifth segments of the legs. 
1. Zeuctodesmus ceruleus, sp.n. (Tab. XIV. figg. 5-57.) 
Colour (in alcohol) a paler or darker Prussian-blue, with a yellow patch upon the upper side of the keels; 
head and antenne blackish ; labrum, legs, and sterna ferruginous, the legs sometimes greenish. 
Head smooth. Antenne shortly hairy. Dorsal surface smooth ; lateral surface of segments granular. Sterna 
and legs thickly hairy. Phallopods with distal segment subcylindrical, terminating in two diverging 
branches, an outer and an inner—the inner longer and stouter, directed obliquely forwards; the outer 
thinner, more pointed, and projecting downwards ; the segment somewhat sharply angled at the base of 
these two processes in front. 
Length, 2, 27 millim., width 7-5. 
” 3, 25 ” ” 7. 
Hab. Muxico, Amula in Guerrero 6000 feet (H. H. Smith). 
Subfam. XYSTODESMINA. 
Aystodesmide, Cook, Ann. N. York Acad. Sci. ix. p. 5 (1895). 
The only character known to me by which the genera referred by Cook to the family Xystodesmide can be 
distinguished from the genera constituting the Chelodesmide of that author is the presence of a spine 
projecting from the distal end of the second segment of the legs. It appears to me that no more than 
subfamily rank should be accorded to this character. 
The Central-American genera have characteristically formed biramous phallopods. The principal or seminal 
branch lies in the same line as the long axis of the proximal portion of the femoro-tibial segment and is 
much longer than the auxiliary or accessory branch. It is generally more or less curved, is hairy in its 
proximal and smooth in its distal half, a longer sensory seta marking the origin of the smooth portion on 
the inner side. The auxiliary branch rises not far from the base of the main portion of the segment on 
its upper side and is directed forwards, or forwards and upwards. It varies in length and is not 
uncommonly spiniform. On the inner aspect of the proximal portion of the segment there is a deep 
groove, overhung below by bristles, which traverses the segment up to the concavity formed by the 
point of origin of the two branches. In the posterior or proximal end of this groove the distal extremity 
of the coxal calcar lies. The groove is the same as that found in the Rhachodesminz, in which, however, 
the coxal calcar is absent. 
The phallopod forcibly recalls that of some of the species of Spheriodesmus and suggests kinship between the 
genera. 
The name Xystodesmine is derived from Xystodesmus, a generic term proposed by Cook for the Japanese 
species described by Peters as Fontaria martensit. 
