1320 



CRUSTACEA. 



wanting, and the antennas are actually three-jointed, the basal joint in 

 this case not extending along the front of the head. 



In the Dichelestidae, as in the Ergasiloidea, these antennae are 

 terete, and four- or five- to seven-jointed. 



The posterior antenna are short organs, consisting of two or three 

 joints, the last either bent into a hook at the extremity, or furnished 

 with short claws, or else curved and set with teeth along the margins ; 

 these different means adapting it for attaching the animal in its para- 

 sitic life. There is often a stout spine at base, directed backward ; and 

 also exterior to the base, or connected with it, another curved or hooked 

 spine. This last spine may perhaps correspond to a second branch of 

 these organs; for in Argulus, there is a terete second branch, of 

 three or four joints, occupying nearly the same position, being just 

 posterior to the stout hooked portion. This hooked joint has on its 

 posterior side a slender two- or three-jointed appendage; but this 

 appendage appears to be properly the termination of the organ, rather 

 than a separate branch, for the branch always proceeds from the 

 normal second joint, while the hooked portion is normally the third or 

 fourth joint. 



These antennae are sometimes very different in the two sexes. In 

 Caligi, the males end in a short joint furnished with two small claws 

 (3 b, Plate 92), while in females, this terminal joint is wanting, and 

 the preceding is slenderly prolonged to a bent point (3 b f ) . 



The trunk-formed mouth is either short ovate, with a rounded 

 extremity behind ; or it is long and slender, and gradually tapers to a 

 narrow point. 



When of the ovoid form, as in Caligus (figs. 1 a and p, Plate 93), 

 the trunk is a hollow organ, bounded above and below by distinct 

 membranes, which represent the upper and under lips. It has a 

 lunate opening between the approximate lips (a a and b, fig. lp)- 



The lateral and lower margin of the buccal trunk is formed by a 

 slender bone (c, b, c, fig. lp), which forms a projection at c, where it 

 suddenly curves around inward, and runs backward a short dis- 

 tance nearly parallel with the margin (c, lp 1 ). These bones form 

 the sides to the lower membrane of the cavity of the mouth. At the 

 anterior extremity of the buccal mass within, they are connected 

 with several small bones, which run to the medial line of the mouth 

 (m, I, and n, fig. p\ and r 9 s, t, fig. p\ an under view) ; these bones he 

 either on or in the lower membrane of the mouth. No portion of the 



