PLATYRACHUS. 143 
those of P. tristant and agree with Carl’s description of them. ‘I'he armature of the lateral borders of the 
keels is as in P, tristani and not as in P. fraternus. The dorsal surface shows distinct traces of the 
polygonal areas so noticeable in such a species as P. clathratus, Gerv., from Bogota, and the granulation 
is less distinct than in P. tristani. The phallopod, judging from Carl’s figure, although very like that of 
P. limonensis, P. fraternus, and P. tristani, has the sublaminate distal portion less expanded. 
Length, 2, 90-100 millim., width 17-20. 
» ds, 90 » » 17 
Hab. Costa Rica!, San José (Biolley®), La Palma 1600 metres (Biolley, Tristan), 
Carrillo ( Underwood). 
It is highly probable that this form, as Brélemann has suggested, will prove to be 
the same as the earlier, but insufficiently described Platyrachus python, Peters, which 
also came from Costa Rica (Hoffmann). The single female upon which the species 
was based measured 100 millim. long and 41 millim. wide. The colour appears to be 
the same as in P. bivirgatus, but Peters says that the dorsal surface is smooth and 
without conspicuous granulation. As I have elsewhere pointed out, however, old and 
large examples of a species of this group are commonly much smoother than smaller 
and younger individuals. Hence the differences mentioned may merely be a matter 
of age. 
7. Platyrachus riparius. 
Platyrrhacus riparius, Carl, Rev. Suisse Zool. x. p. 641, t. 12. fig. 83 (1902) °. 
Colour dark brown above, with the borders of the keels paler ; ventral surface and legs pale brown. 
Female with dorsal surface more strongly vaulted and keels more sloped than in the male, which is flatter. 
Thickly granular above, more coarsely on the posterior than on the median segments, the former also 
showing more distinctly the three rows of small tubercles. Sometimes vestiges of polygonal areas 
observable. No tubercles on the head. eels wide, except those of the anterior three and posterior four 
segments, projecting at right angles to the long axis of the body ; their anterior border straight or lightly 
convex, unarmed; anterior angle blunt; lateral border nearly smooth, lightly sculptured or armed 
with from two to five low blunt tubercular teeth; posterior border from the 5th to the 16th segments 
nearly straight, serrulate; posterior angle from the 7th to the 16th segments bearing a short, blunt, 
small, somewhat inwardly-directed, sometimes spiniform tooth. Pores far removed from the lateral 
border. Caudal process quadrate, with parallel sides. Sternal areas unarmed. Phallopod stout, espe- 
cially at the base, ending in two branches, the seminal stile shorter than the outer auxiliary branch, 
which is sickle-shaped. 
Length 55 to 60 millim., width 11. 
Hab. Costa Rica, Rio Général, Pacific slope (Biolley), 
Although this species has the pores remote from the edge of the keels, in the forn 
of the phallopod it more nearly resembles P. montivagus. 
8. Platyrachus montivagus. (Tab. X. figg. 7-7 4.) 
? Platyrrhacus mexicanus, Attems, Denk. Akad. Wien, Ixviil. p. 348 (1900) * (? P. mexicanus, Lucas). 
Platyrrhacus montivagus, Carl, Rev. Suisse Zool. x. p. 662, t. 12. figg. 84-88 (1902) *; Brélemann, 
Aun. Soe. Ent. France, Ixxiv. p. 342 (1905) ®. 
I have described below at some length the specimens I refer to this species, namely, a series obtained by 
