RHACHODESMUS.—PARARHACHISTES. 177 
yellowish-white, with traces of the bluish tint on the cylindrical portion of the segments. Head finely 
rugose, naked and sulcate above, hairy below. Antenne hairy, not incrassate. First tergal plate almost 
as wide as the second, with lightly concave anterior border, convex lateral border, and posterior border 
straight mesially, directed slightly forwards laterally, the angles rounded. Body elongate; dorsal surface 
rugulose from the 1st to the 18th segment, hollowed, the keels standing high on the sides and a little 
uptilted. Keels subquadrate, slightly wider basally than the median area ; the lateral border excised in 
its posterior half, giving rise to a median lobe and a short posterior lateral subspiniform process ; in the 
- anterior half of the body there is also a small antero-lateral spiniform tooth; keels of 17th and 18th 
segments forming wide spiniform processes, those of the 19th very small. All the leys slender and richly 
hairy. In the male the seminal processes of the coxe of the legs of the 2nd pair are elongate and 
smaller, but somewhat similar processes are present upon the coxe of the 3rd pair. Base of the distal 
segment of the phallopod swollen, thickly hairy inferiorly (posteriorly), and defined from the distal portion 
by a deep notch, giving rise to a conical process, the distal portion straight, not bent downwards, with 
rounded antero-inferior angle and divided into four more or less distinct lamellew, the two inner with 
serrate edges, behind the distal of the latter arises a short process tipped with four long bristles. 
Length, 3, from 50-60 millim., width from 6-7. 
Hab. Mexico, Orizaba 1~°, 
PARARHACHISTES, gen. nov. 
Head with deep frontal sulcus, smooth above and hairy below. Antenne long and slender, not incrassate, the 
4th and 5th segments serrate, only a little shorter than the 6th, which is subequal to the 2nd and 3rd. Keels 
well developed on all the segments, rising high on the sides, and horizontal or more or less elevated at the 
anterior end of the body ; except at the anterior end not in contact, but separated much as in Ihacho- 
desmus and Strongylodesmus; rather longer antero-posteriorly than the median dorsal area of the 
segments ; the lateral margin not noticeably excised, but markedly thickened, especially on the pore- 
bearing segments, which are of the normal number; a small antero-lateral tooth; the 17th to the 19th 
keels posteriorly produced, spiniform, but not sharp. Caudal process of anal segment triangular, trun- 
cated ; anal sternal plate triangular with rounded apex. Sterna wider than long, hairy. Legs long, hairy, 
6th segment shorter than 8rd and about as long as the 4th and 5th taken together. Generative orifice 
- of 2 very large, with two long, generally protruded vulval sclerites. Phallopod of male much like that 
of Lhachodesnus, but with a longish, slender, flagelliform process arising from the base of the distal 
; segment instead of a conical process. 
Ty pe, P. elevatus. 
Distribution. Mexico. 
Allied to Rhachodesmus, Cook, but at least distinguishable by having the lateral 
margins of the keels considerably thickened, the thickening carrying the pore, with 
the edge evenly rounded and nearly straight, at most slightly sinuous and with a 
minute antero-external tooth. 
The two known species of Pararhachistes may be distinguished as follows :— 
a. Keels of the anterior four segments strongly elevated and produced backwards 
far beyond the posterior border of the median area of the segments . . . . elevatus. 
a’. Keels of the anterior four segments moderately elevated and scarcely produced 
backwards beyond the posterior border of the median area of the segments . ._ vertebratus. 
BIOL. CENTR.-AMER., Diplop., December 1909. 2A 
