1889 .] 
213 
[Packard. 
We still need more specimens of this fossil, in order that we may 
determine whether it is a Caratiocaris, as we have formerly regarded 
it, or a Dythyrocaris, to which Prof. J. M. Clark has referred it, 
or whether Rachura is an independent genus. What is preserved 
of the carapace shows that it is, at least, quite different from that of 
Mesothyra. The abdominal segments are sculptured much as in Cer- 
atiocaris ; but the surface of the carapace itself when well preserved 
shows white, stellate enamel-like spots on a dark ground. Such a 
structure of the carapace has not, so far as we are aware, been no- 
ticed by previous observers, in this group. 
Palceocaris typus Meek and Worthen. In one specimen from * 
Mazon Creek, Morris, 111., the antennae of the first and second pair 
on one side are so well preserved as to show their relative pro- 
portions and the entire length of their flagella. The outer, or first 
pair (antennules), are somewhat longer than represented in the res- 
toration (PI. hi, fig. 1), being between ^and^-as long as the whole 
body. Only one branch or division of the flagellum is preserved, 
and probably this is the lower or longer division, of which the 
basal joints only are shown in the restoration of this crustacean. 
The second antennae are well preserved throughout their entire 
length, the flagellum is very long and slender and extends to the 
end of the last segment of the abdomen, hence the second anten- 
nae were probably as long as the body, exclusive of the terminal 
abdominal appendages (uropoda). The number and shape of the 
joints of the scapes of both pair of antennae are as represented in 
the restoration. 
Another specimen shows distinctly that the different joints of 
the scape of both pairs of antennae were provided with numerous 
stiff dense setae ; these have not hitherto been revealed in any 
specimen previously examined and hence are not represented in 
the restoration. 
There are also traces of large well developed second antennal 
scales, like those in the female of Petalophthalmus armatus , but 
larger and broader, well rounded at the end, and extending nearly 
to the end of the scape ; these scales show no traces of setae or 
spines in this specimen, but in another what appears to be an an- 
tennal scale is edged with fine very distinct setae. 
There are also traces of what may possibly be the outlines of 
stalked eyes, but they are very uncertain, and present no traces 
of facets. 
