AMERICAN PARASITIC ARG ULIDJE— WILSON. 701 



Order COPEPODA MuUer. 



Of small size, with an elongated body distinctly segmented, except 

 in degenerate parasitic forms. Head carapace often fused with the 

 first thoracic segment. Four or five pairs of biramose rowing legs on 

 the thorax and an abdomen without appendages. 



[KWTtri^ =an oar, ttovs, = foot.) 



Suborder BRANCH lURA Thorell. 



A flattened body, consisting of a shield-shaped cephalothorax in 

 which the lirst thoracic segment is fused with the head, a free tho- 

 rax of three segments, and a two-lobed abdomen without segments. 

 Four pairs of swimming feet, long and furnished with two rows of 

 plumose setse. Two large compound eyes, movable and surrounded 

 by a blood sinus. Testes in the abdomen. Heart present. Females 

 without ovisacs; eggs attached to foreign objects. 



{ppdvxioc = giWs, ovpa = tai[.) 



Family ARGULIDAE Midler. 



The single family so far known of course possesses the same charac- 

 teristics as the suborder. {Argulu.s — 'A, diminutive of Argus in allu- 

 sion to the number of parts in the compound eyes.) 



ARTIFICIAL KEY TO GENERA AND SPECIES. 



[The relative size of the anterior maxillipeds and the abdomen are expressed in decimal fractions; 

 the former are fractional parts of the width of the carapace, the latter of the entire length of the 

 animal, exclusive of the abdomen.] 



I. First maxillipeds modified into sucking disks. 



II. Two pairs of antenna', the anterior armed with stout lio<jks; preoral sting 

 present Argulus 



II. Only one (the posterior) pair of antenna'; no preoral sting Clionopeltis 



I. First maxillipeds with barbed claws ; no sucking disks ; no preoral sting Dolops 



ARGrLUS. 



A. Carapace lobes overlapping the base of the tail. 

 B. Anterior swimming legs with a fiagellum. 

 C. Carapace orbicular, wider than long. 



D. Teeth of basal plate wide and l)lunt, swimming legs reaching (•onsideral)ly 

 beyond the edge of the (carapace. 



1. Diameter of sucking disks, 0.25; spines on antenna reduced in number, small 



and weak; abdomen relatively very small and orbicular catostomi, p. 709 



2. Diameterof sucking disks, 0.15; spineson antenute large and strong, reinforced; 



abdomen very large and broadly cordate americanus, p. 718 



D/ Teeth of basal plate narrow and sharp; swimming legs not reaching the 

 edge of the carapace. 



3. Abdomen very small, 0.1, orbicular, with wide l)lunt lobes; sucking disks 



0.2 to 0.25 vattcrcrl, female, p. 720 



