PLATYRACHUS. 139 
Keels of mid-region of body not narrowed externally, quadrate, with anterior border projecting at right angles 
to the long axis of the body, with marked anterior angle and long lateral border parallel to the long axis 
of the body ; upper surface of metazonites closely and finely granular; the rows of tubercles faint ; the 
first tergal plate evenly convex, not sunken in the middle; the anterior and posterior borders scarcely 
elevated, the keels but little developed, not directed forwards, the widest point of the plate being about 
the middle ; the pearl-like tubercles but little developed on this and the succeeding terga. Antenne short, 
in 2 second segment only a little longer than the first, its length less than twice its thickness. Legs also 
short ; third segment only a little exceeding the width of the sternal area ; sixth segment not so tapering 
and markedly wider at its distal end than the width of the claw. Phallopods arcuate, curving inwards 
and crossing at the distal end, which is markedly upeurled ; sternum of sixth segment excavated, especially 
posteriorly, to receive them. 
Type, P. scaber, C. Koch. 
Distribution. Costa Rica and the northern countries of South America. 
Analytical Key to the Central-American Species. 
a. Pores remote from the lateral edge of the keels. 
a’. Lateral edge of keel with about five large spiniform teeth ; colour said to be as 
in P. bilineatus . ee ee ee ee ew mexticanus. 
b'. Lateral edge of keel with rounded or sharp tuberculiform teeth. 
a’, Dorsal surface with two narrow pale stripes on a dark ground . . . . .  bilineatus. 
b?, Dorsal surface not so coloured; phallopod strongly bent at its distal end ; 
seminal stile short, sharply bent forwards; auxiliary branch wide, 
laminate (except in P. riparius). 
a’. Dorsal surface yellow, with a dark brown band extending on each side at 
base of keels . 2. 1. 1. Lo woe ew ew ee wes  Oivirgatus. 
b°. Dorsal surface altogether brown, or brown with the whole or part of the 
keels yellow. 
a‘, Auxiliary branch of phallopod sickle-sshaped . . . . . . . « . miparius. 
b*. Auxiliary branch of phallopod laminate. 
a’. First tergal plate with its circumference studded with tubercles . . limonensis. 
b°. First tergal plate with at most a row of indistinct tubercles on its 
anterior and posterior borders. 
a°®, Only the outer half of the keels yellow; their lateral edge with 
five or six pointed tubercular teeth . . . 2. 1. . we. fraternus. 
b°, The entire upper surface of the keels yellow; their lateral edge 
with very low and small, mostly elongated tubercles. . . . . éristani. 
b. Pores near the lateral edge of the keel, their distance from it from twice to less 
than once the diameter of the pore-area; phallopods less strongly curved 
distally than in species mentioned under 4”, with the seminal stile longer and 
the auxiliary branch sickle-shaped. 
a’. Brown, with yellow keels; less convex. 
a’. Keels somewhat strongly toothed like those of P. mevicanus . . . . « montivagus. 
_ Keels with tubercular lateral border. . . . an . . propinguus. 
. Colour almost as in P. bivirgatus, yellow with a brown stripe on each side 
strongly convex. 2. 1. we ee ee stenopterus. 
2 
