RHYSODESMUS. 205 
18. Rhysodesmus fraternus., 
Polydesmus (Fontaria) fraternus, Sauss. Linn. Ent. xiii. p. 323 (1859)'; Mém. Soc. Phys. Genéve, 
xv. p. 310, t. 3. fig. 16 (1860) *. 
? Fontaria fraterna, Attems, Denk. Akad. Wien, Ixviii. p. 260 (1900) °. 
Colour chocolate-brown, with the postero-lateral portion of the keels, the anterior border of the first tergal 
plate, the legs, and antenne flesh-coloured. Body robust and compact; the eels squarely truncated, 
with the lateral margins scarcely swollen. Pores smaller than in R. montezume, to which this species is 
said to be closely allied, and situated more forwards; also the keels of the 17th to the 19th are subacute 
and less rounded than in 2. montezwme ; and the anal valves are striated as in R. fraternus. 
3. With keels sensibly more elevated, and approaching the horizontal in the posterior half of the body; behind 
the 6th and 7th segments projecting a little at the base posteriorly, and having the posterior angle 
somewhat acute. The pores more forward as in R. montezume. 
Length, 9, 37 millim., width 9. 
” 3, 35 ” ” 9. 
Hab. Mexico’, in the villages of the eastern slope of the Cordillera !?. 
This species is said to be closely related to &. montezume, of which it has the 
appearance, the shape, and the colours; but differs in being stouter and in the other 
characters mentioned in the diagnosis. 
I cannot decide whether Attems correctly determined as &. fraternus the female 
specimen in the Hamburg Museum, ticketed Mexico, which he assigned to that 
species. 
19. Rhysodesmus limax. (Tab. XV. figg. 1, 1 a.) 
Polydesmus (Fontaria) limax, Sauss. Linn. Ent. xiii. p. 312 (1859)'; Mém. Soc. Phys. Genéve, 
xv. p. 312, t. 2. fig. 10 (1860) ’. 
Colour chocolate-brown, the keels often paler. Body large, broad and compact. Dorsal surface evenly 
convex; anterior end elliptically narrowed. first tergal plate with lateral angles narrowed ; posterior 
border of segments 2 to 4 lightly concave in the middle area, the posterior border of their keels 
oblique and a little sinuous, the anterior border rounded. eels of the other segments depressed, almost 
following the slope of the dorsum ; anterior border and angle of the keels forming an almost semicircular 
curvature, the border prominent ; the posterior border sinuous, with a convex prominence at the base, 
then directed obliquely forwards, with the posterior angle somewhat produced, so that the entire border 
presents a sinuous ~-shaped curve; as far back as the 10th or 11th segments the keels are directed 
slightly obliquely forwards; only from the 12th are they directed obliquely backwards; marginal 
thickening very flattened, small, shining, posteriorly spiniform on the segments behind the 8th; 
posterior angle of keels of 18th and 19th sometimes deprived of spiniform process. Pores superior, in 
the anterior half of the marginal thickening as far back as the 16th segment. Dorsal area of segments 
1 to 3 smooth, with only insignificant strie, that of the rest with somewhat squamiform sculpturing, which 
becomes coarser upon the keels, the scales becoming as it were spiniferous. In addition the keels 
commonly show traces of three rows of small smooth tubercles ; 18th and 19th segments almost smooth. 
In large individuals the sculpturing becomes almost effaced upon the middle of the back. 
dg. With dorsal surface less vaulted. 
Length 50-80 millim., width 17-20. 
Hab. Mexico, Cordova, San Andres Tuxtla! °. 
In the British Museum there is a single male specimen, probably referable to this 
species and purchased under the name “ P. limaz.” It is 7d mm, long and 22 wide. 
