PERIDONTODESMIDA.—PERIDONTODESMUS. 135 
clavate, and the first tergal plate has an anterior row of granules—features which are 
also possessed by Peridontodesmus. ‘The latter, however, is obviously a more primitive 
type, as is shown by the small size of the first tergal plate and the width of the sternal 
areas; and it may well be that Peridontodesmus is allied to the ancestral type from 
which Cryptodesmus is descended; but since no intermediate genera are, so far as I 
am aware, known, and since the structural differences between them are considerable, 
I see no course open at present but to regard Peridontodesmus as the type of a distinct 
family. 
PERIDONTODESMUS. 
Peridontodesmus, Silvestri, Ann. Mus. Genova, (2) xvi. p. 197 (1896) ; Attems, Denk. Akad. Wien, 
— Ixviii. p. 358 (1900). 
Integument coriaceous. Head without frontal sulcus. Antenne rather widely separated, moderately long, 
incrassate to the sixth segment, which is much the largest of the series, third segment much longer than 
the second or fourth. first tergal plate transversely subelliptical, much wider than the head, but not 
covering it anteriorly ; its anterior edge finely, its lateral angle more strongly toothed. eels of the 
other segments large, horizontal, high on the sides, so that the dorsal surface is moderately flat, with 
untoothed anterior border and strongly toothed lateral and posterior borders ; the metazonites with three 
transverse rows of small setiferous tubercles; a shallow groove lying between the first and second rows ; 
a few small setiferous tubercles on the upper side of the keels; the large marginal teeth also bearing 
setee. Pores normal in number, but small and placed just above the edge of the postero-lateral 
tooth. Anal tergal plate triangular, pointed, the terminal portion not constricted. Valves flattened, 
lightly convex above, flattened inferiorly ; margins very feebly thickened. Anal sternal plate wide, sides 
strongly converging, posterior border straight ; sete widely separated. Sternal areas longer than wide, 
but not narrow. Legs with second segment long, nearly as long as the third, which is shorter than the 
sixth. 
Phallopods with coxal segment very large, fused anteriorly to its fellow of the opposite side, with 
long curved calcar in the normal position and a second calcar projecting inwards from its outer edge; 
distal segment very stout at the base, narrowed distally and tapering into a longish flagelliform process ; 
attached to its lower surface there is a stout, crescentically curved rod, which tapers posteriorly into a 
shorter flagelliform process and anteriorly into a much longer and thinner curved flagellum. On the 
inner side of the thickened portion of the distal segment there arises a subcylindrical piece which projects 
forwards at first, then narrows and curves abruptly downwards on the inner side of the two forwardly 
directed flagella, is sinuous distally, and ends in a point. This is probably the seminal style. Genital 
processes of second leg of male short, with blunt apex. 
Type, P. woodranus. 
Distribution. CENTRAL AMERICA. 
The male-characters of the typical species of this genus, P. woodianus, are 
unrecorded, those given above being taken from the males of the species from 
Guatemala described below. Hence it is impossible to know which features they 
present have a specific and which a generic value. 
Key to the Species. 
a. Antero-lateral tooth of the keels, except at the posterior end of the body, 
large, acute, and projecting as far laterally as the pore-bearing tooth ; 
lateral border of keels of second with four teeth . . . . . . . + + flagellatus. 
