1914.] NATURAL SCIENCES OF PHILADELPHIA. 43 



the two developed apical setae, the inner longer one is to the outer 

 as 10 : 7. Schmeil shows both of these setae to be evenly plumose 

 on their distal seven-eighths. This character is rarely present in the 

 specimens from this vicinit^^ The anterior plumose portion is 

 replaced by a short row of delicate spines on either side of the setae 

 (PL III, fig. 7) . These do not merge into the hair-like forms gradually, 

 but end abruptly at the beginning of the plumes as in the long 

 median caudal seta of C. phaleratus. The lateral spine is inserted 

 two-thirds of the length of the stylets from their anterior border. 

 It is usually delicately plumose, although the bare form is not rare. 



The female first antennae may have either eleven or twelve seg- 

 ments. The number given by Schmeil is twelve, but I have frequently 

 found eleven-jointed sexually mature forms, bearing eggs. Such 

 forms occur more frequently in late winter and the twelve-jointed- 

 antennae forms in April and May (PI. Ill, figs. 6 and 8). The antennae 

 are a little over two-thirds as long as the first thoracic segment. 

 The division from eleven to twelve joints takes place in the third 

 joint. The fourth, fifth and sixth joints are often narrower than 

 the seventh and eighth. Most of the antennal bristles are not 

 plumose. Schmeil notes the presence of a well-developed, closelj^ 

 lying sense-club on the ninth segment. This I cannot discover on 

 the specimens that have come under my observation. In its place 

 there is a minute sensory (?) hair. 



The first antennae of the male are peculiar in the unusual develop- 

 ment of the sensory structures of the first division. These are 

 larger than in any other species of the genus and may be readily 

 noted even under a slight magnification as long blue, semi-transparent, 

 narrow bag-shaped structures on the posterior side of the antennae. 



The swimming feet are all two-jointed. The outer ramus of the 

 fourth pair is generally visible from above in life. This is due to 

 the unusually large lamella connecting these feet which makes them 

 protrude at a greater lateral angle. Schmeil notes that the fourth 

 pair of swimming feet is less fully developed than the other three 

 pairs. In fig. 11 of PI. Ill I have shown a foot of the third pair. 

 It is interesting to note an indication of the third segment; a row of 

 .short hairs at the middle of the distal segment of the outer ramus 

 and a group of longer hairs on the corresponding segment of the 

 inner ramus. This character is always present in the first three 

 pairs of swimming feet. 



The armature of the swimming feet is as follows: 



First pair — outer ramus, three spines, five setae; inner ramus, one 

 seta, one spine, four setae. 



