1897] POSSIL APODIDAE 408 
of these larger eyes are two spots. These are also found on another 
specimen, part of which is shown in figure 5, copied from Dr 
Schuchert’s paper. In Apus in front of the paired eyes is a median 
pore (fig. 6, p.) leading into the water sac, in which these paired 
eyes are now sunk. In the base of the channel leading from this 
pore to the water spaces above the eyes a body called the median 
eye is suspended. The structure of this eye and its probable origin 
—as suggested by its structure—out of a pair of anterior eyes I 
have discussed elsewhere. It is therefore of some interest to me 
to find an animal, with such claims to be a relative of Apus, having 
a pair of what appear to be eyes in front of the usual pair. It is 
true that this anterior pair persists in Limulus, but here again the 
relationship between Apus and Limulus is still matter of discus- 
sion. It is therefore once more pleasant to find what appears to be 
a direct confirmation of one’s morphological deductions in an animal 
certainly related to Apus. What the peculiar ovals round these 
anterior ‘ eyes’ are in fig. 5 it is impossible to say. It may be that 
here we see these eyes being drawn into the median line and below 
the surface. . 
In Protocaris I should regard the two eyes, suggested in figure 
1, as corresponding with the paired eyes of Apus: perhaps owing 
to the bending of the carapace they are sunk deeper in the water 
sacs, 
I quite agree then with Dr Schuchert in calling these early 
crustaceans fossil Apodidae. Protocaris I suggest is a modifica- 
tion of Apus in the direction of the bivalve Ostracods, Dipeltis 
as a second attempt of a true Apus to adopt the Trilobitic modi- 
fication of repeating the head shield as pleurae along the trunk 
segments, while preserving for some reason or other the habit of 
Apus. Henry M. BERNARD. 
1 « Apodidae,” pp. 100-111. 
