qe 
STENODESMUS. , 187 
The two Central-American genera of the group may be readily distinguished as 
follows :— 
a. Pores present only upon the fifth segment; the two branches of the phallopod 
enormously long as compared with the palmar * portion, which is only about 
half the length of the auxiliary branch . . . . 1... . SC. )0CSTENODESMUS. 
a’. Pores normal in number; the two branches of the phallopod shorter, the 
auxiliary branch usually much shorter, never longer than the palmar portion 
ofthe segment . . . . . 2. ee ew ee wee ee ew |) CRE goDESMUS. 
STENODESMUS. 
Stenodesmus, Saussure, Linn. Ent. xii. p. 827 (1859); Mém. Soc. Phys. Genéve, xv. p. 539 (1860) ; 
and of subsequent authors. 
Related to Rhysodesmus apparently in all essential features, even in the form of the phallopod, but with the 
pores absent from all the segments, with the exception of the fifth. According to Carl, the terminal 
segment of the phallopod has a single superior auxiliary branch, which is long and slender and projects 
parallel with the main or seminal branch, but falls considerably short of its apex; it rises close to its 
base. The main or seminal branch is long, lightly curved, and hooked at the tip. 
Distribution. Mexico. 
1. Stenodesmus mexicanus. 
Stenodesmus mexicanus, Sauss. Linn. Ent. xiii. p. 327 (1859)'; Mém. Soc. Phys. Genéve, xv. 
p. 589, t. 3. fig. 21 (1860) *; Carl, Rev. Suisse Zool. xi. p. 561, fig. 20 (1903) *. 
Colour maroon-brown, with the edges of the keels, the legs, and the underside yellowish. 
Head with frontal sulcus well marked. Lirst tergal plate with its anterior border slightly elevated and defined 
by a shallow groove. Dorsal surface convex, the keels following approximately the slope of the median 
portion ; sculpturing very distinct, consisting of longitudinal strie and scattered granules, the latter 
disappearing upon the keels. eels of segments 2 to 4 with their posterior border directed obliquely 
forwards; their posterior angles not spiniform; those from the 6th backwards with their posterior 
border emarginate and posterior angle spiniform, the spiniform process much in evidence on segments 8 
to 13 and becoming gradually less marked on segments 14 to 18, rounded on segment 19; the anterior 
border on the 8th and following segments directed obliquely backwards; the anterior angle rounded ; 
lateral border with linear thickening and very finely denticulated. Caudal process conical ; anal sternal 
plate rounded, with median tubercle as well as the normal setiferous tubercles, 
3 rather smaller than the 9, with the sculpturing coarser, the dorsal surface less convex, and the posterior 
tooth of the keels less acute and produced. 
Length, 2, 65 millim., width 12. 
» 36,40 ,, » 10. 
Hab. Mexico, Cordova !~°, 
* I have used the term “palmar portion” in this key and the key of species of Rhysodesmus for the 
proximal grooved portion of the distal segment of the phallopod, the length of this area being Judged from the 
inner aspect of the segment, 
