138 . DIPLOPODA. 
Subfam. PLATY RACHINA. 
Typical members of the family with the pores opening upon the upper side of the keels, sometimes close to the 
lateral edge, sometimes remote from it, and not insunk in distinct depressions, but surrounded by a thick 
circular rim, giving them the appearance of a cannon’s mouth. Lateral edge of keels never smooth and 
thickened as in most Polydesmoidea, but generally narrow and granular, like the rest of the upper side 
of the keel. 
Distribution. Central America (Costa Rica); West Indies; northern part of South 
America; Oriental Region east of Tenasserim. 
The Central-American representatives of this group known to me fall into two 
well-marked sections, one of which is represented by a single species, the other by a 
considerable number. For the former I adopt the name Tirodesmus given by Cook 
to an allied form. For the latter I retain the old name Platyrachus, C. Koch, of 
which the type, P. scaber, Koch, came from Brazil, and resembles in general features 
the species here referred to that genus. It must be remembered, however, that the 
generic diagnosis here given of Platyrachus was not taken from the type-species, in 
which the secondary sexual characters of the male and other important features are 
unknown, but from the Central-American forms enumerated below. Of the latter, 
however, I have seen representatives of only six out of the ten species. In the case 
of the remaining four, the descriptions given by their describers are not sufficiently 
detailed to supply the information necessary to give assurance as to their agreement 
in all respects with the diagnosis of the genus Platyrachus given below, and it is 
possible that disagreement from it may be found to occur in one or more minor 
points. This, however, would by no means necessarily involve exclusion of such 
deviating species from the genus; it would only necessitate modification of the 
generic diagnosis to meet the discrepancies. 
The two genera may be contrasted as follows :— 
a. Phallopods arcuate, incurved and crossing at the apex, which is strongly 
upcurled, the sternum of the sixth segment excavated to receive them; keels 
of mid-region of body quadrate, with anterior border projecting at right angles 
to long axis of body, and with convexly rectangular anterior angle; legs and 
antenne very short. . . . 2. 2 1 1 ee ew ee ee ee ee) PATYRACHUS. 
b. Phallopods subparallel, projecting straight forwards, not apically upcurled ; 
sternum of sixth segment in ¢ not excavated; keels aliform, the antero- 
lateral border forming a nearly continuous arch directed obliquely outwards 
and backwards, and uninterrupted by any marked anterior angle; legs and 
autenne much longer. . . . 2 eee ee ee ee ee) OT RODESMUS. 
PLATYRACHUS. 
Platyrachus, C. Koch, Syst. Myriap. s. 181. 1. itl. Bandchen zu (Panzer) Herrich-Schiaffer, Krit. 
Revis. Insektenfaune Deutsch]. 1847; Die Myriapoden, i. p. 47 (18638). 
Polydesmus (Stenonia), Saussure, Mém. Soc. Phys. Genéve, xv. p. 581 (1860). 
Platyrrhacus, Attems, Brélemanu, Carl (in part.). 
