RHYSODESMUS. . 201 
11. Rhysodesmus smithi, sp. n. (Tab. XV. figg. 12, 12 a.) 
2. Colour doubtful, probably with the metazonites and prozonites brown, the keels certainly mostly yellow ; 
first tergal plate apparently all brown, except the keels; head brown; antennz yellowish-brown, darker 
apically ; legs pale yellowish. . 
Antenne short; width of head about equal to length of segments 2-5. 
First tergal plate nearly semilunar in shape, the lateral portion of the anterior border only slightly oblique ; 
lateral portions of posterior border also only slightly oblique. Body smooth, shining, convex, with scarcely 
if any trace of tubercles on the keels. eels small and depressed, not or hardly overlapping when the 
segments are contracted ; ridge of the anterior border produced, if at all, at the anterior angle, which on 
the segments in the middle of the body is rectangularly rounded; lateral margin lightly rounded ; 
posterior border nearly straight, scarcely produced, inclined backwards from about the 15th segment; 
posterior angle blunt, nearly rectangular, only a little produced on the 17th and 18th segments; 
marginal thickening somewhat lozenge-shaped on the pore-bearing segments ; pores on the fifth in the 
middle of the margin, behind the middle on the other segments. Jnterzonal groove complete, shallow 
dorsally. Sterna scarcely wider in front, mesially depressed behind, laterally notched. Zegs with distal 
segments considerably longer than penultimate. 
$3. Smaller and narrower, but with keels relatively much larger, their posterior angle square and subacute. 
Phallopods as figured, and as described in analytical key (anted, p. 194). 
Length, ?, 30 millim., width 6+; length of antenne 5 millim. 
” 3» 25 ” ” 5 3 ” ” ) ” 
Hab. Mexico, Omilteme in Guerrero 8000 feet (H. H. Smith). 
12. Rhysodesmus arcuatus, sp. n. (Tab. XV. figg. 13-13 e.) 
@. Colour deep blackish-brown ; keels externally yellow, at least with a large yellow spot around and 
extending inwards from the pore, the anterior angle and extreme posterior edge of the keels brownish ; 
anterior keels yellower than the posterior ; caudal process yellow; head dark brown; antenne brown; 
legs yellowish-brown, with terminal segments clear yellow ; sterna and lateral surface brownish. 
Antenne moderately long ; width of head about equal to segments 2+3+4+half of 5 or over. 
First tergal plate with its anterior border only lightly convex in the middle line, generally lightly produced 
where it passes into the obliquely sloping nearly straight lateral portion ; lateral angle moderately wide, 
rounded; posterior border mesially nearly straight, laterally also nearly straight but oblique. Body 
broad and compact, the keels overlapping. eels moderately large, scarcely following the slope of the 
dorsal surface, which is often somewhat wrinkled and bears distinct scattered tubercles on the keels ; 
anterior border of keels convex, the ridge defining it curved forwards in such a way that its most prominent 
point is about halfway along the keel; anterior angle obtusely rounded and forming an even curve with 
the lateral edge; posterior border a little produced, lightly sinuous or lightly convex, inclined slightly 
forwards in the anterior half of the body, beginning to incline backwards from about the 15th 
segment ; posterior angle mostly nearly rectangular, acute on segments 15 to 19; the marginal thickening, 
which is tolerably large, even, and not abruptly expanded round the pore, sometimes a little produced 
posteriorly. Pores lying near the middle of the lateral margin, looking slightly upwards. Jnterzonal 
sulcus continued right round the segments. Sterna mesially depressed, laterally notched, wider in front 
than behind. Legs with distal segment moderately long and slender, longer than the penultimate. 
3. Flatter; the keels approaching the horizontal. Phallopods as shown in figure and as described in 
analytical key to species. 
Length, 2, 38 millim., width 10; length of antenne 7 millim. 
” 3d; 35 ” ” 85; cB ” 75 ” 
Hab. Mexico, Omilteme in Guerrero 8000 feet (H. H. Smith). 
bX 
o 
BIOL, CENTR.-AMER., Diplop., Apri/ 1910. 
