CALIGOIDEA. 



1315 



antennae are simple, and more or less hooked or prehensile ; the first 

 pair of legs are slender pediform organs j the second pair are stout and 

 prehensile. The species in one of these two sections, the Caligim, 

 have a broad peltate body, the anterior segment or shield covering a 

 large part of the whole ; and the second antennas are very short and 

 stoutly hooked, and concealed beneath the body. In the other section, 

 the Dichelestid^e, the body is narrow ; the anterior segment is com- 

 paratively short ; and the second antennas are elongated, and project 

 beyond the head. 



The Dichelestidae are related to the Ergasilidse in some of their 

 characters ; and yet are more closely similar to the Caligidse. The 

 structure of the maxillae, buccal trunk, and first pair of legs (or max- 

 illipeds), is much like the same in the Caligidse; the natatory legs 

 have little of the perfection of those of Ergasilus, they approximating 

 in the form of the four anterior, and in the abnormal character of the 

 four posterior, to the structure in the Caligus type. 



These characters, together with the tubular form of the oviferous 

 appendages, fix their relations to the Caligidse. 



The Caligidae exhibit a relation to the Corycaeidae, and especially 

 to the flat Sapphirinae, in their hooked second antennae, and the general 

 character of the legs, including the prehensile form of the second pair 

 (the second pair of legs corresponding normally to the first pair in 

 that family). This affinity is also strikingly seen in the fact that 

 some species have the spectacle-eyes of the Sapphirinae and Corycsei, as 

 detected by the author. 



The Argulidae are similar to the Caligidse in their posterior an- 

 tennae ; but they are more remote from the Corycaeidae than either 

 the Caligidae or Dichelestidse, since the anterior antennae are wanting; 

 the legs which correspond to the first pair in the Corycseidse are not 

 prehensile ; the females carry no external bags or tubes of eggs. The 

 division Peltocephala of Edwards, which includes the Argulidae and 

 Caligidae and excludes the Dichelestidae, is not therefore retained in our 

 system. The mere form of the body, as shown in the Corycaeidae, is a 

 character of inferior value. 



The three families mentioned may be characterized as follows : : — ■ 



Fam. I. Argulidae. — Corpus late depressum, peltatum. Antennae 

 lmae obsoletse. Pedes lmi tubulati, 2di unguiculati. Ova in tubis 

 vel sacculis externis non gesta. 



