1897] FOSSIL APODIDAE 403 



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. Tn 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. 1 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. Henky M. Beknakd. 



1 "Apodidae," pp. 100-111. 



