'I'rin rth r iis /!<<■/,/. — Heechev. 41 
arc shown on Plate [ii, figures 8, 9. No essentia] differences 
have been observed in the series attached to the free - 
ments. Each segment bears a pair of luminous appendages, 
originating at the sides of the axis, as in other trilobites 
(Walcott, I. <;.). The anterior legs are the longesl and the 
others gradually be< e shorter towards the pygidium. 
Those which are here taken for description are the legs of 
the second and third free thoracic segments. The entire 
length of the legs has been exposed from the dorsal side, by 
removing- the overlying pleura' of the thorax, which concealed 
nearly half their length. Each limb consists of two nearly 
equal members, one of which was evidently used for crawling 
and the other for swimming. These two members and their 
joints may be correlated with certain typical forms of crusta- 
cean legs among the Schizopoda, Cumac'ea, and, Decapoda, 
and may be described in the same terms. Therefore each 
limb is composed of a stem, or shaft, with an outer branch 
(exopodite), and an inner branch (endopodite). Plate in, 
figure 9, shows the joints of the stem (6, 7), the exopodite 
( ex, 1 and 2), and the endopodite (en, 1-5). The precise 
form of the coxal joint of the stem (coxopodite) has not yet 
been clearly made out. It is followed by a broad joint about 
twice as long as wide, which may be referred to the protopo- 
dite. 
The endopodite (figure 9, en) was the member used for 
crawling, as in the Schizopoda. The three proximal joints 
(5, 4, 3) are similar in form to (>, and taper gradually out- 
wards. The distal portion is completed by two slender cylin- 
drical joints (2, 1), the latter bearing at its extremity short 
seta', or bristles, of which three are commonly to be seen. 
The other member, the exopodite (ex), lies over the endop 
odite. It apparently articulates with the protopodite, but 
may spring from what is here referred to the coxopodite. as 
its basal portion is very broad and originates close to the 
articulation of the protopodite with tl >xal joint. The 
proximal joint of the exopodite (2) is somewhat arched and 
tapers rapidly. 1 1 extends to the ends of the pleura', and i- 
the longest joint of either branch. The posterior edge is 
finely denticulate, ami carries a row of long setae. The distal 
portion (1) is mul Particulate, being composed of ten or more 
