RHYSODESMUS. 197 
directed obliquely forwards; from the 11th to the 16th becoming gradually more in line with the 
posterior border of the segments, and from the 17th directed obliquely backwards. Anal sternal plate 
triangular, Sternal areas wider in front than behind; rather deeply notched and sulcate laterally ; not 
flat in front; posteriorly emarginate, almost bitubercular. Legs with spine strong; terminal segment 
moderately long, but barely twice as long as the penultimate. Phallopod with its smooth terminal 
portion inclined slightly inwards when viewed from below ; lightly sinuous from its lateral aspect, with 
the tip turned upwards ; the auxiliary branch directed obliquely forwards and upwards. 
Length of ¢ about 40 millim., width 9; length of antenne 7 millim. 
Hab. Mexico, the plateau of Anahuac and the mountains rising from the plateau 
(Saussure }?), Peak of Orizaba (Mus. Brit.). 
I do not think there is any reason to doubt the correctness of my identification of 
the specimen in the British Museum which I have described as R. totanacus. It 
agrees very closely with Saussure’s description and figure of that species, the colour 
especially being exactly the same. 
3. Rhysodesmus pusillus, sp. n. (Tab. XIV. figg. 7, 7a; XV. fig. 9.) 
3. Colour (in specimen available) uniformly brown or testaceous. F%rst tergal plate with anterior border nearly 
straight, transverse in the middle; at the sides obliquely cut away, not forming a continuous curve 3 
posterior border laterally oblique, meeting the anterior in a blunt acute angle. Dorsal surface smooth? 
with a few granules laterally, convex. eels rising about the middle of the side, depressed, with their 
anterior and lateral margins somewhat strongly raised, especially round the anterior angle, which is 
strongly rounded and salient (rather more prominent, that is to say, than the posterior angle), so that the 
lateral border is inclined slightly inwards from before backwards; the ridge defining the anterior border 
without any abrupt forward curvature, straight from the base of the keel to the curve of the anterior 
angle ; posterior border of keel straight, inclined slightly forwards at the anterior extremity of the body, 
transverse in the central portion and backwards from about the 17th segment ; somewhat thickened and 
uptilted and defined by a notch from the posterior border of the median portion of the segment; a wide 
groove passing in front of the keel defining the prozonite from the metazonite. Pores on anterior and 
median segments nearly in the middle of the lateral border. Sterna longer than wide; transversely 
sulcate, laterally notched and mesially depressed in their posterior half; posterior border straight or 
lightly emarginate. Legs thickened, terminal segment much longer than the penultimate and armed 
with a long stout claw; spine of second segment short on the anterior and median segments of the body. 
Phallopod with distal segment short, thickly hairy internally ; the terminal ramus, when viewed from 
below, projecting straight forwards and sharply incurved at the tip; when viewed from the side the tip 
is seen to be slightly downcurved as well; accessory branch very short, slender, and hooked. 
Length about 20 millim, width about 4. 
Hab. Mexico (Mus. Brit.). 
In size this form shows resemblance to &. vicinus, Sauss.; but, on the evidence 
supplied by Saussure’s description of that species, it is impossible to affiliate the two. 
According to that author, 2. vicinus is very closely allied to R. otomitus, the figure of 
which gives a good idea of the form of R&. vicinus. If that be so, f. pusillus differs 
essentially from £. vicinus in the form of its keels, for the figure of &. otomitus does 
not show the obtuseness of the posterior angle of the keels, the prominence of the 
anterior angle, the obliquity of the lateral margin, and the sloping character of the 
keels so noticeable in &. pusillus. 
