SPH ERIODESMUS. 123 
segment widely extended laterally; distal segment short but very stout, biramous; the inferior branch 
broad, sinuously curved, with rounded spatulate apex, bearing inferiorly a short membranous process 
which is probably the seminal style; a long, thinner subsidiary branch projecting upwards and 
forwards. 
Length 27 millim., width 9-5. 
Hab. Mexico, San Andres Tuxtla in Vera Cruz. 
Although from the same locality as the preceding, and presenting the same colour 
and much the same shape of keels, this species differs essentially from it in its 
secondary sexual characters, as shown by the structure of the anterior legs of the male, 
of the phallopods, and of the rim of the socket in which the phallopods are lodged. 
These organs show that although the females might be difficult to distinguish, the 
males are widely divergent. 
5. Spheriodesmus prehensor, sp.n. (Tab. VIII. fige. 9, 9a.) 
In the shape of the body, the form of the segments and of the keels, very similar to S. robustus from San 
Andres Tuxtla, but much smaller and of a uniform whitish-grey colour. The lateral portions of the 
fourth and fifth segments are subequal in width, and on the fifth the marginal groove is continued along 
the inferior edge and upcurled at the posterior angle. 
First leg of male but little modified, the femur (third segment) without tubercle and not excavated inferiorly. 
Sterna of fifth and sixth of about the same relative width as in S. oniscus; but the rim of the socket 
of the phallopods a little raised laterally carrying up the spiniform tubercle, the elevated edge gradually 
subsiding just in front of the coxal segment of the posterior legs of this segment of the body, which are 
separated by a sternal area about equal in width to the length of their second segment. Phallopods with 
basal segments stout, widely separated proximally but converging distally, with a tubercle on their 
anterior face; the distal (tibio-femoral) segment short and stout, biramous, the principal branch spatulate 
aud bearing two short slender processes at the apex, the inner or inferior of these the larger of the two 
and hooked; the smaller or accessory branch rising from the lower side on the inner edge of the segment 
and blade-like and polliciform. 
Length 15 millim., width 5. 
Hab. Mexico, Omilteme in Guerrero 8000 feet (H. H. Smith). 
4, Spheriodesmus angustus, sp.n. (Tab. IX. figg. 1-1 9.) 
3. Colour (in alcohol) pale olivaceous. Body noticeably narrowed posteriorly and gradually sloping down- 
wards from about the sixteenth segment, not abruptly sloped quite at the posterior end. Segments 
smooth, shining. eels of fourth segment with pronounced sigmoid curve, the anterior border strongly 
convex, the posterior correspondingly concave ; keels of fifth slightly wider except at the extremity than 
those of the fourth. The posterior borders of the majority of the keels lightly convex and marked off from 
the dorsal portion of the segments by a slight notch, which becomes more distinct towards the posterior 
end of the body. The posterior angles of the keels from the sixth to the tenth segments rounded, from 
the eleventh to the fourteenth rectangular, from the fourteenth to the nineteenth becoming gradually 
more and more acute ; posterior border of keel of eighteenth segment forming a decided angle with the 
posterior border of the dorsal portion of the segment. Anal tergal plate nearly as long as wide. 
First leg of male a little modified, the femur hollowed on its inferior edge, with a low basal anguliform 
prominence. Sterna of fifth and sixth segments noticeably narrower than the length of the second 
segment of the legs. Socket of phallopods extending laterally almost to the spiniform tubercle, where 
its rim is a little raised and thickened, the rim not raised posteriorly. Sternal area between the legs 
of the posterior pair of the seventh segment narrow, about equal in width to the length of the second 
segment of the legs. Phallopods with basal segments not strongly convergent, distal segments stout, 
R2 
