1X48 CRUSTACEA. 



yellowish posteriorly. The cephalic segment is very distinct. The 

 posterior acute angles of the cephalothorax are rather short. The 

 position and general characters of the anterior antennas are nearly as 

 in the P. crispata, and if it is possible that the crispata has in its most 

 advanced state, acute angles behind, the two species may perhaps be 

 identical. The hairs towards the base of the antennae are crowded as 

 in that species, but none I believe are uncinate ; the apical setae are 

 also shorter. 



The pigment of the inferior eyes, as seen in a vertical view, is a 

 nearly round blue-black spot behind the superior eyes. The abdomen 

 has four segments, the first of which is a little the largest, and the fourth 

 the smallest ; but they vary in relative proportions. The caudal setae 

 are about as long as the abdomen; the stylets are a little longer than 

 broad. There are about eighteen joints to the anterior antennae ; the five 

 terminal are short and subequal ; the anterior subapical setae are hardly 

 longer than the diameter of the joints. The second joint of longer branch 

 of posterior antennae is one-third to one-fourth the preceding in length. 

 There are four pairs of natatories, the anterior smallest. The longer 

 branch, in all four pairs, three-jointed, the shorter two-jointed. There 

 is also a fifth pair, much smaller and naked, with two minute spines 

 at apex of longer branch. 



In the posterior part of the cephalothorax, either side of the in- 

 testine, there is an oblong deep blue gland. 



Specimens were collected in the Atlantic which are probably 

 identical with the above. The abdomen is only two-jointed, the 

 second very short: but this organ varies much in the same 

 species. There are only three posterior segments to the cephalo- 

 thorax ; a posterior fourth was not distinctly observed ; yet the poste- 

 rior angles were acute, as above. Pigment of superior eyes carmine- 

 black, separate. Anterior antennae about as long as body ; setae as 

 above described. Posterior antennae have the second joint of longer 

 branch not one-fourth the length of the first joint ; the setae are nearly 

 as long as the branch. 



The maxillipeds were observed to be employed in giving the body 

 a leaping motion, while the animal was under the microscope without 

 sufficient water to swim. First pair of legs two-branched, one branch 

 consisting of five slender joints ; the other of two stout joints, and 

 bearing three or four long spinulous setae. Natatories four pairs; 



