44 BRITISH PARASITIC COPEPODA. 



freedom of locomotion, closely approaching in some cases 

 that of the normal free-swimmers ; usually however their 

 movements appear to be more or less restricted. They retain 

 their position on the fish, at least to a considerable extent, by 

 means of the strong terminal hooks with which certain of 

 their appendages are furnished, such as the second pair of 

 antennas, the maxillipeds, and one or two others. 



The young leave the eggs as free-swimming nauplii. 



The Caligoida comprise the three families Caligida3, 

 Dichelestiidas, and Philichthyidas, the first two of which are 

 represented by a considerable number of genera and species. 



Family n. Caligiile. 



Carapace tolerably broad, more or less flattened, 

 provided with, anterior frontal plates. Free thoracic 

 segments uncovered or sometimes more or less con- 

 cealed by paired dorsal plates. Antennules small, two- 

 or three- jointed. Antennas forming short, movable, 

 hooked claws. Mouth a suctorial beak formed by a 

 modification of the upper and lower lips, and inclosing 

 styliform mandibles. Second maxillipeds stout, with 

 strong terminal claws. First four pairs of thoracic 

 legs all biramose, or the first and fourth pairs may be 

 uniramose. Fifth pair rudimentary. Eyes median, 

 contiguous, sometimes obsolete. Egg-strings two, 

 usually elongated. 



The male is generally smaller than the female. 



In some genera the mature stage is preceded by that of the 

 chalimus, or young stage, which is temporarily fixed to the 

 host bv a more or less elongated slender frontal filament (cf. 

 PI. IV," figs. 3-5). 



Genus 4. CALIGUS 0. F. Milller, 1785. 



Carapace large, flattened, shield-like. Frontal plates 

 provided with small but conspicuous sucking-disks or 

 lunulas. Fourth pair of thoracic legs uniramose. Fifth 

 pair rudimentary, and very small. G-enital segment 

 in the female usually expanded and moderately large. 

 Abdomen short or moderately elongated and composed 



