PLATYRACHUS. 14] 
tergal surface, &c., and there appears to me to be very little doubt that he had in his 
hands examples of the species to which Carl subsequently gave the name P. montivaqus. 
3. Platyrachus tristani, sp.n. (Tab. X. figg. 6-6 0.) 
3. Colour black, with the entire keel yellow, so that the yellow area on each side of the upper surface is equal 
in width to the black area; head black; antenne and legs brown, with their two basal segments and the 
ventral surface clearer yellow-brown. 
Frontal area of head granular, with two large tubercles. Dorsal surface very distinctly granular, much more 
coarsely so than in P. montivagus, and in consequence much less shining; the rows of tubercles traceable 
only on the posterior segments. First tergal plate with its angle rectangular and blunt; the border in 
front of the angle very obscurely tuberculate. eels better developed than in P. montivagus, a little 
higher on the side, and nearly horizontal, so that the dorsal surface is flatter. The lateral margins of all 
the keels only very slightly irregular, owing to their being studded with small shining tubercles—in no 
sense of the word describable as teeth. Anterior border of the keels lightly convex and forming an 
even curve with the convex anterior angle; the posterior border straight or, at the posterior end of 
the body, lightly concave; from about the 7th to the 17th segments the posterior angle is a little 
produced and spiniform, very feebly so on the anterior of these segments and not strongly so on those of 
the postericr half of the body; posterior angle of the 18th sharp, of the 19th rounded. Pores remote 
from the margin, as in P. mevicanus; lateral edge of some of the pore-bearing keels with a shallow 
indentation, which, however, never extends nearly so far as the pore; anterior border of keels from 
about the 13th to the 18th very finely serrulate, and the posterior border from about the llth. Second 
tergal plate with its posterior angle more produced and more square than in P. montivagus. Caudal 
process semicircular. Anal sternal plate narrower than in P. montivagus, with the tubercles much 
larger and separated by a narrower space. Sternal areas of body slightly hollowed out, but neither 
longitudinally nor transversely sulcate ; each furnished with four low tubercles in the posterior half of the 
body, but in the anterior half these are more pronounced, being especially well developed upon the 5th, 
8th, and 9th; on the sternum of the 6th, which is excavated, the anterior tubercles are large and the 
posterior absent ; and there is a very distinct pair at the base of the legs of the 7th segment. A small 
conical tooth on the sternum of the 4th. Rim of cavity of phallopods with a groove just below it, as in 
P.montivagus, Phallopods a little less strongly bowed in their proximal half than in that species, so that 
there is a narrower space between them; distally crossed; the upcurved portion sublaminate, blunt, 
with sinuous edges; the seminal stile very short and slender and turned forwards in a direction nearly 
at right angles to that of the sublaminate auxiliary portion. 
Length of g 94 millim., width 14. 
Hab. Costa Rica, La Palma (7Zristan). 
Closely allied to P. limonensis, Attems, and P. fraternus, Carl; but the descriptions 
given of the typical examples of these two species compel me to regard the example 
above described as representing a form distinct from both. As regards P. limonensis, 
Attems says that the circumference of the first tergal plate is studded with larger 
tubercles, that the keels of segments 2 to 4 are “nach ruckwarts gezogen,” that the 
colour is chestnut-brown, and that the basal segments of the legs of the sixth pair are 
furnished with a long conical process (“* Zapfen”’). This last is a very remarkable 
character, if it exists in reality. Can it be that Attems has mistaken the rather long 
vertical sternal process for a coxal outgrowth ? Apart, however, from this, the other 
characters enumerated are sufficient to enforce the separation of P. tristani from 
P. limonensis. 
With regard to P. fraternus, this species was separated by Carl from P. limonensis for 
