184 DIPLOPODA. 
a very short auxiliary branch ; fossa of phallopods very small, its width barely one-fourth the diameter of 
the prozonite, its posterior border remote from the coxx of the ambulatory legs of the seventh segment. 
Type, P. ornatus. 
_ Distribution. Mexico. 
~The two forms here referred to Pammicrophallus, together with the single species 
belonging to the genus described below as Zeuctodesmus, exhibit the extreme stage in 
the degeneration of the phallopods exemplified by the Central-American species placed 
by Carl in the Rhachodesmine. The first stage is the suppression of the coxal calcar 
shown in Strongylodesmus, Rhachis, and others, in which the phallopod is otherwise 
round, except for the presence of a pit or excavation on the inner side of the distal 
segment. The second stage is shown in the typical form of Aceratophallus, in which 
there is no definite pit on the phallopod, the two segments of which are axially in the 
same straight line, though the phallopods remain normal as to size; the final stage 
being reached in the two genera here described as new, in which the phallopods, 
though in some respects like those of Aceratophallus, are greatly reduced with respect 
to size, the socket that lodges them being comparatively diminished both in length 
and breadth. 
The males of the two species referred to the genus Pammicrophallus may be readily 
distinguished as follows :— 
a. Phallopod slender, ending distally in two slender processes, a longer and a shorter ; 
the margin of the fossa raised in front as wellas behind. . . . . . . . .~ ornatus. 
a’. Phallopod laterally bicarinate and expanded, its apex compressed and ending in a 
simple point ; the margin of the fossa only raised behind . . . . . «© « . pictus. 
1. Pammicrophallus ornatus, sp.n. (Tab. XIV. figg. 3-3 7.) 
2. Colour (in alcohol) of fresh specimens variegated *, a median dorsal yellow spot usually visible, the keels 
yellow, sometimes clouded in front, between the keels and the pale spot dark brownish or bluish ; head 
and antennsx generally darker than the legs. 
Head smooth, with frontal sulcus. Antenne short and hairy, moderately long, scarcely incrassate; second, 
third, and sixth segments subequal and a little longer than the fourth and fifth. Body moderately robust 
and wide, smooth and polished above. Keels well developed, but, except on the anterior segments, not 
‘overlapping; almost horizontal, slightly uptilted posteriorly ; 1st tergal plate as wide as the 2nd, 
evenly convex above, its keels being depressed with widely rounded anterior and nearly rectangular 
posterior border; posterior angles of keels of 2nd and 3rd rounded, of 4th very slightly produced; from 
the 5th to the 19th gradually more and more produced, but blunt, not sharp, the posterior border 
lightiy concave; anterior border nearly straight, inclined gradually more and more backwards towards 
the posterior end, but the backward inclination never strongly marked, the anterior angle always well 
emphasised, rather larger than the angle of a square, with a small external tooth which is present on all 
the keels from the 2nd backwards; margins of keels slightly thickened, but comparatively markedly so on 
the area around the pores. Anal tergal plate triangular, but apically truncate; anal sternal plate triangular, 
but with apex rounded. Sternal plates a little narrower behind than in front, their posterior border 
concave, transversely sulcate laterally. Lateral surface of segments nearly smooth; no distinct crest 
even on the anterior segments, above the base of the legs. Legs slender, in the mid-region of the body 
oe * When dried or after many years’ immersion the pattern fades away entirely or almost so. 
