1086 Wisconsin Academy of Sciences, Arts, and Letters. 



The furcal rami are rather slender, nearly equalling in 

 length the last two abdominal segments. The lateral seta is 

 at about one-half the length of the ramus. Of the terminal 

 setae, the outer is short, while the inner one is rather un- 

 usually long. 



The first antennae (PL LXXV, fig. 7) are long, exceeding the 

 second cephalothorax segment. The antenna is composed of 

 seventeen segments, the twelfth bearing a sensory club. The 

 terminal segments of the antenna have no special armature. 



The spinous armature of the terminal segments of the exo- 

 podites of the swimming feet is 2, 3, 3, 3. 



The fifth foot consists of two segments. The length of the 

 first segment is rather less than twice its breadth; it bears on 

 the outer distal angle a long seta. The second segment is 

 twice as long as broad ; on its outer distal angle it bears a seta ; 

 on its inner distal angle, but set back a little from the end, it 

 bears a slender serrate spine or seta ; this inner spine nearly 

 equals in length the outer seta. 



The form of the receptaculum seminis is shown in the figure 

 (PL LXXV, fig. 9). 



The females are about 1.1 mm. in length. 



This was found in Calabasas, in southern Arizona. 



C. tenuis resembles, in its form, C. Leuckarti, but differs in 

 the form of the fifth feet, in the lack of armature on the an- 

 tennal segments, and of crenulatons on the outer maxillipede, 

 and in the form of the receptaculum seminis. 



It seems to be most nearly related to the European oitho- 

 noides. I at first thought it should be a variety of that species. 

 The difference in the form of the fifth foot, however, with the 

 lack of antennal armature and the somewhat different re- 

 ceptaculum seminis have led me to consider it a new species. 



