1883, | 179 {Packard, 
the Polydesmidee is seen in the head of Polydesmus ocellatus Pack. and P. 
cavicola Pack., both American forms. 
The Hyes. When well developed the eyes are equilaterally triangular, 
d.¢., the ocelli are arranged in a triangular area ; in Lystopetalum lactarium 
there are 40-41 facets arranged in rows. In Cryptotrichus cwsioannulatus, 
where the eye is also developed, there are about 24 facets ; as several of the 
species inhabit caves, and suffer a partial or total loss of eyes, there is 
much variation in the number of ocelli; in Psewdotremia cavernarum the 
eyes are irregularly linear ; the ocelli being arranged in about four irregular 
groups, with 11-19 ocelli, the number of ocelli varying in different indi- 
viduals of the same species. In Trichopetalum the ocelli vary from 10-19. 
In Scoterpes and Zygonopus the eyes are entirely wanting. In those eyes 
which are partially aborted, there are a few partly developed ocelli, less 
than half as wide as, and scattered irregularly among, the normal ones. 
The Antenne. These are much longer and slenderer than in any Julide, 
and more nearly resemble those of the Polydesmidse than the former 
family ; but differ from both groups in the much longer terminal joint, 
and in the decided inequality in the relative length of the joints, the third 
and fourth joint being much longer than the others ; the number of joints 
in our American species being invariably seven (not counting the basal 
undeveloped eminence to which the first joint is attached). The antennx 
are longest and slenderest in Pseudotremia and Lysiopetalum, and shortest, 
in Scoterpes, Zygonopus and Trichopetalum. 'The joints are more setose 
in Trichopetalum, and least so, perhaps, in Scoterpes. In all the genera 
there are from two to four flattened, enlarged, broad, fusiform tactile hairs 
situated on the end of the terminal joint. As observed in Lysiopetalum 
and Pseudotremia, these hairs are two-jointed, the basal joint short and 
broad ; they are filled with granules like the material filling the spaces in 
the nervous fibres between the nerve-cells in the terminal antennal joint, 
which is nearly filled with nerve fibres and very small nerve-cells, show- 
ing that the antenns must be very sensitive tactile organs, especially in 
the blind forms. 
The Arthromeres. The body-segments of the Lysiopetalidee have a defi- 
nite family form and style of ornamentation. In Lysiopetalum and Pseu- 
dotremia all the scutes are ornamented with numerous longitudinal ridges, 
which end in a point overhanging the depressed, flattened portion of the 
scute; in Pseudotremia, which is a modification by cave-life of the first 
named genus, the ridges are more or less obsolete and replaced by flattened, 
coarse granulations, and the lateral swellings of the scutes are well devel- 
oped. 
In all the other genera, the scutes are not thus ridged, and the lateral 
bosses or swellings are distinct; in all except Cryptotrichus, the bosses have 
three setiferous, acute tubercles arranged in an irregular triangle; in Cryp- 
totrichus the tubercles are further apart, arranged almost in a straight 
