NO. 1788. NORTH AMERICAN EROASILID^— WILSON. 355 



the basal joint not much stouter than the two terminal ones and armed 

 with a large spine at its distal end. The second and third joints are 

 of the same size, the third one roughened over its entire surface and 

 tipped with a narrow conical process at the outer distal corner, a 

 thickened claw at the inner corner, and about five long curved and 

 sharp-pointed claws over the rest of the tip. 



The upper lip is very wide anteriorly, contracted and with a 

 reentrant curve posteriorly; it is one-third wider than long (fig. 104). 



The mandibles are three-jointed, long, slender, and simple; they 

 start out vertically, then bend at a right angle and extend inward 

 to the mouth opening, parallel with the surface of the head; the ter- 

 minal joint is short and not toothed. 



The first maxillae are reduced to mere knobs, each bearing three 

 plumose sctge. The second maxillse are short and two-jointed, the 

 terminal joint bipartite, the posterior branch longer than the anterior, 

 both with smooth and acuminate tips. The maxillipeds are much 

 enlarged and are attached diagonally behind and outside of the other 

 mouth parts, not reaching as far forward as in Bomoloclius, but not 

 directly behind the other parts as in TseniacantJius. 



The basal joint is more or less rectangular and attached to the sur- 

 face of the head except at the very tip; the terminal joint is in the 

 form of a stout chitin claw with a swollen base and a blunt tip. This 

 claw has somewhat of an S-curve, but not very pronounced, and has 

 no teeth or projections (fig. 115). 



The cephalothorax is joined to the fused thorax by a neck, formed 

 of the second thorax segment, which varies much in length in different 

 individuals, but is usually very short. The second pair of swimming 

 legs are on this segment and in close proximity to the first pair; each 

 ramus is two-jointed and the joints are about the same size, the ter- 

 minal one well armed with setae. The endopod is apparently always 

 carried flattened back against the basal joint where it is often very 

 difficult to find it. 



The fused thorax or trunk is made up of the third, fourth, and 

 fifth joints; it is oblong and so much swollen that the thickness is 

 fully eqvuil to half the width; the corners are evenly rounded and 

 project posteriorly in the form of lobes; the lateral margins and the 

 posterior margin between the lobes are somewhat emarginate. On 

 the dorsal surface there is a third lobe in the center between the other 

 two and about the same size. There are four pits or depressions on 

 the dorsal surface of this swollen trunk, and four others upon the 

 ventral surface. The former are arranged at the four corners of a 

 square, the latter in pairs on the median Ime, the two anterior ones a 

 little closer together than the two posterior. In the ventral pits are 

 to be found the rudimentary third and fourth legs; each consists of 

 a somewhat swollen basal joint and two rami; the exopod is two- 



