240 TRANSACTIONS OF THE [May 22 
cylindrical leg, and the other is thin, broad and leafy, with what 
seems to be a comb-like structure similar to the gills of many 
crustacea. These branchiz, if so they be, depend from a nar- 
row, thickened anterior edge or limb; they seem to correspond 
with two of the three cephalic (?) legs shown in the specimen, 
and to overlie them. By analogy with Mr. Walcott’s determina- 
tions, they are probably attached to the basal joints of the leg. 
In Figs. 2, 3 and 6 are shown the ends of appendages, which 
projected from under the carapace, and seem to belong to the 
thoracic region. These are likewise of two kinds, one of which 
shows an oblique comb-structure or system of parallel lines 
(see Figs. 2, 2*, 3and 4); and the other is a strong tapering leg, 
with three cylindrical or slightly flaring joints visible (see Figs. 
2, 2°, 3,5 and6). The first may be a branchial appendage ; it 
is flat and appears to broaden into a small paddle at the tip, 
though this appearance may be deceptive ; it has a sharp ridge 
and narrow furrow along the anterior edge, and behind that, the 
series of lines or comb-like structure, which may be due to the 
remains of hairs or gill-structure on the limb. 
Figure 4 shows a series of appendages of both kinds, but 
very poorly preserved. In Fig. 7, the projecting appendages of 
the tail-piece are shown, and it may be seen that apparently 
several, and perhaps all of the pygidial limbs are anchylosed, so 
as to make a rounded flap, which in shape, though not in strue- 
ture, reminds one of the telson of a crayfish, and perhaps served 
the same purpose—to propel the animal backwards through the 
water. 
The conclusions as to the nature of these appendages are 
only provisional, and may be much changed by further discov- 
eries. They are not nearly as well preserved as the antenne, 
nor in so considerable a number of specimens ; as besides those 
figured, there are only two or three others which show them at 
all, and those, only traces: The shape and structure of the sup- 
posed branchiz, in particular, are very hard to distinguish ; the 
figures given, however, represent, as far as I can see, the actual 
outline preserved, 
It will be seen that the structure of Zriarthrus must have 
differed not a little from that described by Mr. Walcott in Caly- 
mene and Ceraurus. The presence of antenne, the broad, 
leafy gills, and the anchylosed flap under the pygidium (provid- 
ing that the two latter are correct interpretations of the struc- 
ture) are all important points of difference, and indicate that 
the Trilobites were quite varied in structure, and probably 
included a number of widely differing forms. If the classifica- 
tion founded on the characters of the shield is not deceptive, 
