446 ON THE STRUCTURE AND AFFINITIES OF HIMANTOPTERUS 



Copepoda ; and M. Milne-Edwards has suggested that Eurypterus 

 possibly holds an intermediate position between the Copepoda and 

 the Isopoda. 



1. If we compare Himantopterus with Apus we find points of 

 resemblance in the form and position of the sessile eyes, — in the 

 position of the antennae and of the great natatorial feet, and, to a 

 certain extent, in their form, — in the structure of the jaws, — and 

 finally, if Apus productus be compared with Hvnantopterus acuminatus 

 and H. bilobus, in the terminal segment. 



The discrepancies, however, are even more striking and important. 

 The number of free segments in Apus is thrice as great as in Himan- 

 topterus ; the carapace extends as a free fold far back over them ; all 

 the thoracic, and the great majority of the abdominal segments 

 possess foliaceous appendages (which would certainly have been 

 preserved in as perfect a state as other similarly constituted parts, 

 had they existed in Himantopterus^ ; and lastly, the penultimate 

 segment carries long articulated styliform appendages. 



2. A certain similarity between Himantopterus and Liniulus in 

 their carapace and eyes, the large size of the terminal segment and 

 the chelate form of the antenna; in both, may be regarded as the 

 most salient resemblances of the two genera. To these might be 

 added a sculpture, not altogether unlike that of Himantopterus, on 

 some parts of Limulus, and a certain resemblance in fundamental 

 structure between the last ambulatory feet of Limulus and the great 

 swimming members of Himantopterus. 



The differences consist in the number and great development of 

 the locomotive members in Limidus, the coalescence of its abdominal 

 segments, their well-developed appendages, and the much smaller 

 total number of segments. 



3. Himantopterus resembles many Copepods in the form and 

 relative proportions of the carapace and free segments, in the sessile 

 position of the eyes, in the great locomotive antennae and post-buccal 

 appendages, and in the absence of the majority of the abdominal 

 appendages. 



But the thoracic appendages are always well developed in the 

 Copepods, and the number of free segments is never so great as in 

 Himantopterus. 



While the relations of Himantopterus with the Pcecilopods, Cope- 

 pods, and Phyllopods, then, must by no means be overlooked, they 

 Would appear not to be sufficiently close, while the differences, on the 

 other hand, are too numerous to justify its arrangement in either of 

 these families. 



