176 DIPLOPODA. 
Rhachidomorpha aduncus, Attems, Denk. Akad. Wien, Ixvii. p. 410 (1899) *, 
Rhachis (Microrhachis) uncinatus, Carl, Rev. Suisse Zool. xi. p. 556, t. 16. fig. 15 (1903) °. 
2. Colour cochineal-red, passing into white in dried specimens. Body slendcr, with the segments, which are 
smooth and shining, a little separated. Antenne long. Dorsal surface flat between the keels, which are 
tilted upwards above the horizontal plane. First tergal plate with its anterior border nearly semicircu- 
larly arched, the posterior strongly sinuous, its keels directed backwards and sharp. The other keels 
aliform, becoming more and more pointed and produced posteriorly and terminated by a long spine; 
their anterior edge bordered and armed externally with a small tooth. Pores small, opening on the 
terminal spine. Caudal process of 20th conical. 
¢. Keels much more elevated, segments more separated and the anterior tooth more pronounced than in the 
female. Phallopods with distal segment bent at right angles to the basal (coxa) and stout; its femoral 
and tibial areas not distinctly separable ; from the base distad of the seminal fossa there arises a chitinous 
process bearing the seminal duct, to which the main part of the segment acts as a guard; this is divided 
into two pieces, an inner simple, shaped like a knife-blade, while the outer is expanded, more lobate, 
. and itself subdivided. 
Length, 2, 20 millim., width 2-7. 
3, 21 » «28. 
Hab. Mexico, Monte Azul, Cerro de Azcamela, Sierra de Agua in the Eastern 
Cordillera 1~?. 
39 
According to Humbert and Saussure, this species is difficult to distinguish from 
R. tarasca, but has the keels less divergent, less elevated, less corniform, more 
lamellar, more aliform, and with the anterior border more arched. 
RHACHODESMUS. 
Polydesmus (Rachis), Saussure, Linn. Ent. xiii. p. 3826 (1859); Mém. Soc. Phys. Genéve, xv. 
p. 829 (1860) ; Humbert & Saussure, Verh. z.-b. Ges. Wien, xix. p. 692 (1869); Miss. Sci. 
Mex., Myr. p. 54 (1872). 
Rhachis, Attems, Denk. Akad. Wien, Ixvi. p. 415 (1899) ; Carl, Rev. Suisse Zool. xi. p. 554 
(1903) (preoccupied). 
Rhachodesmus, Cook, Ann. N. York Acad. Sci. ix. p. 4 (1895). 
Antenne long and slender. Dorsal surface flat or even slightly hollow. eels, except those of the anterior 
segments, which are contiguous, somewhat widely separated from each other on each side, wide and 
lamelliform, with the lateral border not thickened, or scarcely so, but irregularly lobate or toothed, only 
to a slight extent thickened round the pores, which are normal in number and placed near the middle of 
the lateral border slightly above the edge. Caudal process of anal segment triangular, truncate. Legs 
very long. Sterna hairy. Phallopods with basal segment (coxa) without calcar: the second segment 
stout but short, swollen basally and furnished internally with a large subcircular seminal fossa which is 
lined with bristles. 
Type, 2. viridis. 
Distribution. Mexico and California. 
1. Rhachodesmus viridis. 
Polydesmus (Rhachis) viridis, Sauss. Linn. Ent. xi. p. 326 (1859)'; Mém. Soc. Phys. Genéve, xv. 
p. 830, t. 3. fig. 19 (1860) 2; Attems, Denk. Akad. Wien, Ixvil. p. 415 (1899) °*. 
Colour blue or green, becoming more or less decolorized in alcohol, the keels, legs, and antenne becoming 
