1855.] HUXLEY — HIMANTOPTERUS. 35 



4. Lastly, many parts of the body of Himantopterus present a 

 peculiar imbricated sculpture, resembling that exhibited by Ptery- 

 gotus. 



Assuming these data to be correct, the question is, — In what group 

 of animals can we find an analogous structure ? and there are obvious 

 reasons for at once narrowing the field of inquiry to the Crustacea, 

 and confining the search to the different subdivisions of that great 

 group. 



Analogies, if not for Himantopterus, at least for the very closely 

 allied genus Eurypterus, have been sought by different naturalists 

 among the Pcecilopoda, the Phyllopoda (particularly Apus), and the 

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

 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 posi- 

 tion 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 

 Apv^ productus be compared with Himantopterus acuminatus and 

 H. hilohus, 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 afree 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 Limulus in 

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

 the chelate form of the antennae 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 oi Himantopterus. 



The differences consist in the number and great development of 

 the locomotive members in Limulus, the coalescence of its ahdominal 

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

 total number of segments. 



3. Himantopterus resembles many Copepods in the form and rela- 

 tive proportions of the carapace and free segments, in the sessile posi- 

 tion of the eyes, in the great locomotive antennse 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 

 Himan top terus. 



While the relations of Himantopterus with the Poecilopods, Cope- 

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



D 2 



