HAEPACTICID^. 3 



be looked upon as the typical form of the family ; the 

 genera which depart from this rule being Zaus, 

 Peltidium, Porcellidium, Idya, and Scutellidium, all of 

 which are to a greater or less extent flattened from 

 above downwards. Amymone, on the other hand, 

 presents a peculiarity of the opposite kind, being flat- 

 tened laterally. The two pairs of antennae do not 

 present any remarkable abnormalities of structure ; 

 the mandibles, however, vary very considerably, more 

 especially as to the degree of development of the palp, 

 which in some cases is reduced to very small dimen- 

 sions (Canthocamptus, Attheyella, Laophonte, &c.) ; 

 the maxillge also vary a good deal in development, and 

 in Longipedia approach very nearly to the shape of the 

 same organs in the Galanidce. The usual digitate, sub- 

 triangular shape of the first pair of foot-jaws is lost in 

 some genera, as in Ectinosoma, Idya, and ScuteUidium, 

 where these limbs are prehensile and clawed; the second 

 foot-jaw constantly takes the form of a powerfully 

 clawed prehensile hand except in the genera Longipe- 

 dia, Ectinosoma, Zosime, and Brady a (sub-family Longi- 

 pediince), where it approaches somewhat to the structure 

 seen in Calanidce and Cyclopidce. The first pair of feet 

 has in general one or both branches adapted for 

 prehension, and more or less powerfully clawed ; but 

 in the genera belonging to the sub-families Longi- 

 pediince, Tachidiince, and Amymonince, it is formed for 

 swimming, being nearly or quite like the following pairs. 

 The second, third, and fourth pairs are always natatory 

 organs, and the outer branches are always 3 -jointed ; 

 the inner branch, however, has a variable number of 



