[5] LAKE SUPERIOR ENTOMOSTRACA. 705 



ing the third pair of legs alone being free. Beneath, however, all the 

 leg-bearing segments except the last are marked off by sternal sutures. 



The head is distinguished by a transverse constriction, but without 

 suture, and the antenna! region is similarly marked off from the re- 

 mainder of the head. The eye is distinctly double in structure, with 

 but little pigment. 



Owing to modification and distortion of the male abdomen (PI. i, fig. 

 1; PI. ii, fig. 7) its segmentation is difficult to make out, but the muscular 

 structure shows that there are but four free segments. Of these the 

 second and third are laterally produced to form a large chela, and the 

 fourth bears the toothed and broadly paddle-shaped processes previously 

 described,* the former of these springing from the ventral portion of the 

 segment and the latter from the dorsal. The base of the right ramus of 

 the furca is concave without to adapt it to these structures, the whole 

 abdomen being evidently strongly flexed to the right when this compli- 

 cated apparatus is in use. There are but three developed plumose seta3 

 at the tip of each ramus, and besides these a short, stout tooth at the 

 outer distal angle, and a delicate simple hair at the inner. 



The autenuse are twenty-five jointed, and reach about to the third 

 segment of the abdomen. The median joints of the female antennae 

 aud of the left of the male are thickened at the articulations, giving 

 them a slender hour-glass form. 



The right antenna of the male is apparently twenty-one jointed, the 

 thirteenth to the eighteenth segments are dilated, and the nineteenth 

 segment is hinged upon the preceding. Both antenna3 are richly sup- 

 plied with sensory structures, which have the form of two- or three-jointed 

 hairs, with very delicate terminal segments, no olfactory clubs occurring. 

 The basal segments of these hairs on the first and third joints are espe- 

 cially large and long, and contain distinct cells and finely granular 

 matter. The terminal joiut of each antenna is lobed at tip, with six 

 long hairs; and there are four such hairs on the penultimate joint. 



The autennules are short, the ramus apparently but three-jointed, the 

 short median joints common in this appendage being only obscurely 

 indicated. The second joiut is as long as both the other two, the first 

 is very short, the third about three- fourths the second. The ramus 

 bears four terminal and four lateral long curved plumose hairs. 



Before the mouth opening is a vaulted labrum, opposed to a similar 

 elevation behiud, the mandibles fitting into the transverse cleft between 

 these lips. 



The mandibular palpus (PI. i, fig. 4) is three-jointed, the first aud last 

 joints very short, each about a fourth of the length of the middle one. 

 The greatest width of the latter is contained about twice in its length. 

 The tip of the palpus bears six long plumose hairs, with a cluster of 

 four shorter ones near it. The ramus is short, twice as long as the third 

 joint, obscurely four-jointed, and bears three long plumose terminal 

 hairs and three longer lateral ones. 



T-r w -.oo ax *Araer, Nat., loc. cit, 



H. Mis. 133 45 



