42 DIPLOPODA. 
- semisuctorial. Terga from the fifth to the penultimate with a pair of lateral scent-glands ; pleural areas 
large, membranous or chitinized; sterna freely movable. Legs with coxal pouches. Both pairs of legs 
of 7th segment modified in the male, externally attached to distinct sternal plates lying in the same 
plane as those in front and behind, short and thick, consisting of six or seven segments, the posterior 
pair, constituting the phallopods, protected apically by the anterior pair. 
Two families of Colobognatha are represented in Central America, viz. the Platy- 
desmide and Siphonophoride, which are diagnosed below. Further research, however, 
will probably reveal the existence in this area of a third family, the Polyzonide, which 
has representatives both in North America, South America, and the West Indies. In 
the structure of the gnathites the Polyzonide are somewhat intermediate between the 
Siphonophoride and Platydesmide, the mandibles being distinct and bisegmented as 
in the latter, whereas the gnathochilarium has lost the distinctness of its sclerites as in 
the former. From both they differ in the form of the head, which is triangular, with 
one or more pairs of eyes and a relatively narrow frontal area between the bases of 
the antenne. Siphonotus, which occurs in South America, has a single pair of ocelli; 
Polyzonium and Octoglena from three to four pairs in a subvertical series. Polyzonium 
has been recorded from Indiana and Tennessee ; Octoglena, which is said to be distin- 
guished from it by the emargination of the anterior tergite and the exposure of the eyes, 
from Georgia [see Bollman, Bull. U.S. Nat. Mus. no. 46, pp. 117, 137, 154, 187 (1893) ]. 
Fam. PLATYDESMIDZ. 
Head broadly cordate, narrowed in the labral region, the edge of which is bluntly pointed. Antenne lateral. 
Mandibles present, bisegmented. Gnathochilarium distinct, narrowed distally, but otherwise departing 
but little from the type characteristic of the Chilognatha, the lingual lobes and stipites with or without 
distinct terminal pieces; mentum large, L-shaped. Terga with median groove, two rows of tubercles, 
and large carine. Pleural area membranous. Penes perforating coxe of second legs. 
Distribution. Mediterranean Region ; Central Asia (Amurland); Malacca, Sumatra; 
United States; Central America. 
PLATYDESMUS. 
Platydesmus, Lucas, Ann. Soc. Ent. Fr. (2) i. p. 51 (1848) (type P. polydesmoides) ; and subse- 
quent authors. 
Piestodesmus, Lucas, Rev. et Mag. Zool. 1849, p. 598 (type P. moreleti). 
Characters as diagnosed below (p. 44). 
Distribution, Central America. 
instead of from the two pairs of the seventh segment. The question must still be regarded as open; and 
Cook’s view may prove correct. But in a male specimen of Platydesmus perpictus I find 76 pairs of legs 
and 38 segments (excluding the last two) behind the phallopods, which gives two pairs of legs to each of the 
segments in question, as in other Helminthomorphous Chilognatha. Whereas, if Cook’s interpretation be 
adopted, this specimen has only a single pair on the last leg-bearing segment. 
