AKT.5. NORTH AMERICAN PARASITIC COPEPODS WILSON. 7 



forward at the anterior corners as if to form a pair of large flow- 

 ing sleeves. 



In Anthoso?}ia, beside the large dorsal carapace over the cephalo- 

 thorax, each thorax segment carries a pair of lateral plates or wings, 

 which overlap like tiles on a roof, and give the parasite a peculiarly 

 bizarre appearance. 



• We may say, then, that the body of a dichelesthiid is made up of 

 four parts or regions, a cephalothorax composed of the head and 

 first thoracic segment fused, a free thorax of from two to four seg- 

 ments, a genital segment either alone or fused with the preceding 

 thorax segments, and an abdomen of one or more segments. For 

 appendages there are two pairs of antennae, a pair of mandibles, 

 two pairs of maxillae, a pair of maxillipeds, and from two to five 

 pairs of swimming legs. 



Antennae. — The first antennae are attached to the anterior margin 

 of the cephalothorax, are cylindrical in form, and are composed of 

 a number of short joints placed end to end and plentifully supplied 

 with setae. Tlie number of joints varies considerably, not merely in 

 different genera but also among the species of the same genus; but 

 since the muscles of these first antennae are poorly developed it is 

 difficult, as Heider has said, to determine just how many segments 

 there are. In his figures of the species of Lernanthropus he repre- 

 sented the antennae as varying from three to nine segments, and a 

 similar variation has been found in the species described by the pres- 

 ent author. Furthermore, the basal joint in some species is enlarged 

 much more than in others. In the different genera the number of 

 joints varies from three in Pseudocycnus and Pseudoclaivella up to 

 nine in Bassettithia and fifteen in Nemesis., the basal ones being in- 

 distinctly separated (fig. 72). 



The second antennae are fastened to the ventral surface of the 

 head close to the anterior margin. Being the chief organs of pre- 

 hension they are large and stout in most of the genera. They are 

 made up of two or three joints, the terminal one in the form of a 

 strong claw which is usually curved, sometimes barbed [Cyhicola) 

 and sometimes strongly chelate {Pseudoclavella., Dichelesthiuni., 

 Kr0yeria). Rarely these appendages are armed with setae only 

 {Lam/proglena., Donusa., Ventriculina). The basal joints are swollen 

 and armed with powerful muscles by means of v>'hich the terminal 

 claws can be driven into the flesh of the host (figs. 4, 24, 32, 78, 98). 



Mouth parts. — The proboscis is formed of an upper and an under 

 lip, which project from the ventral surface of the head. Near the 

 base the margins of the two lips are tolerably parallel and separated 

 by only a slight distance, but each lip soon begins to taper and in 

 consequence the margins diverge. On either side at the point where 



