1126 



CRUSTACEA. 



The anterior antennas in the more typical species are generally very 

 nearly straight, excepting the outward curve at base, and sometimes a 

 forward curve at tip ; and they usually extend obliquely outward, with 

 the extremities much in advance of the line of the beak. Sometimes 

 the two make an angle between them less than 60°. The angle of 

 divergence is an important characteristic of species. 



In the few Calanoid Pontellae the antennae have the double curva- 

 ture of the Calani, and the tips are behind the line of the beak. 



The length of the antennae varies from three-fourths of the length of 

 the cephalothorax, to one and a half times the length of the whole body. 

 In some species, with the antennae shorter than the cephalothorax, the 

 joints are few and rather long (9 to 13); but in others they are 18 to 

 24, and the joints are consequently short. 



Posterior antennae. — The posterior antennae consist of a basal joint, 

 stout and rather short, and two branches. The longer branch has the 

 first joint oblong, and the second quite short, and often appearing 

 double, or, at least, bilobate, each lobe bearing a tuft of long setae ; or, 

 if the lobes are not distinct, all appearing as a single tuft. There are 

 sometimes one or two setae on the back of the first and second joints. 

 The shorter branch is also two-jointed, but, unlike the Calani, the 

 joints are commonly very unequal, and sometimes the apical is ex- 

 tremely short. The Pontelhe are further unlike the Calani in having 

 about five long setae at the apex of this branch, and none on the 

 margin of the first joint. 



In some Calanoid species, the joints of the accessory branch are 

 nearly equal, the apical setae are three in number, and the side seta3 

 exist precisely as in the Calani. In those least Calanoid, the branches 

 are very unequal. This inequality increases almost regularly with 

 the more forward position of the anterior antennae; and where these 

 antennae diverge at 60° or less, the accessory branch is but a fourth 

 the other, or even less than this, becoming almost rudimentary. 



These antennae are used as in the Calani. 



Mandibles. — The mandibles are stout and corneous, with a dentate 

 edge. There appear to be six acute teeth on the cutting edge, besides 

 a seventh, situated a little out of the plane of the others, and in the 

 natural position of the parts, more interiorly. The remaining part of 

 the organ, called the palpus, consists of a large oblong basal joint and 



