332 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



well developed, entering at either end into the sockets of the an- 

 tennae themselves (see fig. 13). 



Basal joints much inflated and reenforced on the inner margin by 

 two stout chitin ribs in each joint; second joint the same length as 

 the basal, but tapering considerably; hinge between second and 

 third joints quite complicated; third joint about the same diameter 

 throughout; fourth joint a short, curved claw, bluntly pointed. The 

 last two joints together are not quite as long as the second (fig. 7). 



The mouth-parts project strongly from the ventral surface in a side 

 view (see fig. 52), with the maxillae at the tip of the projection. The 

 labrum is so thoroughly fused with the head that its outlines are often 

 indistinguishable, but the evenly rounded posterior margin is usually 

 visible. Basal joint of the mandible with a large rectangular outer 

 portion set in a socket of similar shape at the extreme lateral margin 

 of the labrum and just posterior to it, so as to allow the mandible to 

 move forward under the lip. At the inner end the posterior border 

 of this portion is cut diagonally forward and inward, while a deep 

 circular incision is cut out of the anterior border. The narrowed neck 

 between the diagonal cut and the circular incision constitutes the inner 

 portion of the basal joint and is turned forward at an angle of about 

 45 degrees (fig. 27) . To the end of this neck is attached the cutting 

 blade, which is triangular in shape, a little longer than the neck, 

 usually curved forward, and armed along its posterior margin and 

 around the tip with a row of long hairs or spines. The palp is also 

 triangular, its base attached to the diagonal cut on the posterior 

 border of the basal joint, its anterior side fastened for a short distance 

 to the posterior margin of the neck. It also has a row of shorter 

 spinelike teeth along its outer margin. First maxillae reduced to mere 

 knobs, projecting from the ventral surface between the basal joints of 

 the mandibles and those of the second maxillae. From the top of each 

 knob project two stout curved spines, articulated at the base so as to 

 be movable, the outer one a little longer and stouter than the inner, 

 and both plumose. Second maxillae similar to the mandibles except 

 that they have no palps; basal joint of the same width and length, 

 triangular in shape, with the apex pointing inward and narrowed to 

 a short neck which is curved forward. The cutting blade is long and 

 triangular; its anterior margin and the entire ventral surface are 

 covered with a dense growth of bristles. Maxillipeds entirely lacking. 

 Labium reduced to a transverse ridge, its posterior margin nearly 

 straight. Rami of first four pairs of swimming legs three-jointed and 

 well armed with spines and setae. Fifth legs reduced to a compara- 

 tively well-developed sternum, at either end of which in young 

 females is a very short, one-jointed process tipped with two spines; 

 in the fully developed adult the process is wanting and there is but a 



