576 PROCEEDINGS OF THE NATIONAL MUSEUM vol. »♦ 



KEY TO THE SPECIES OF ARGULUS IN THE UNITED STATES NATIONAL MUSEUM " 



a\ Anterior respiratory area prolonged laterally around posterior one (club- 

 shaped). 

 b\ Teeth of basal plate of second maxillae sharp and well separated; sup- 

 porting ril)s of suction cups made up of 12 to 15 singly imbricated 

 segments; tlagellum of first antenna with 2 equal segments; no fliigella 

 on legs; distal segment of third basipod in male with many small 

 knobs on ventral surface but without posterior spine; fourth basipod 



with a single spherical peg stizostethii 



6^ Teeth of basal plate sharp and well separated; supporting ribs of suction 

 cups made up of 10 to 12 doubly imbricated segments; no flagella on 

 legs; basal segment of tlagellum on first antenna five times as long as 

 distal segment ; thii-d basipod in male without knobs but with posterior 

 curved spine; fourth basipod with 2 pegs, the outer one bent at right 



angles canadensis* (p. 568) 



6*. Teeth of basal plate blunt, close together ; supporting ribs of suction cups 

 made up of 4 to 6 segments; flagella present on legs; third basipod 

 with ventral suckers ; fourth basipod without a peg in male ; respiratory 



areas very narrow siamensis 



a". Smaller respiratory area anterior, mesial, or in an anteromesial notch of 

 larger area. 

 6\ Entire smaller respiratory area anterior to larger one. 



c\ Teeth on maxillary plate sharp, distal one more widely separated than 

 other two ; ribs of suction cups composed of 10 to 12 shorter segments 

 and 1 longer one; carapace just reaching fourth segment, which has 

 rounded corners overlapping abdomen ; third basipod in male with 

 posterior swelling; fourth basipod with 2 blunt anterior processes 



and a spherical peg alosae 



c*. Teeth on maxillary plate blunt and close together; ribs of suction cups 

 with 7 to 8 beadlike segments not imbricated ; fourth segment without 

 overlapping corners; carapace reaching abdomen; basipod of second 

 leg in male with 2 posterior processes, of third leg with posterior 



swelling, of fourth leg with an acute peg lunatus* (p. 557) 



c'. Teeth on maxillary plate sharp and curved dorsally ; ribs of suction cups 

 made up of 1 long basal and 6 to 7 short terminal segments flattened 

 but not imbricated ; second and third male basipods not modified, fourth 

 with a spherical peg at anterior center of distal segment. 



longicaudatus* (p. 555) 



c*. Basal plate of maxillae lobed or with slender blunt teeth. 

 d\ Maxillary teeth blunt but plate not lobed. 

 e\ Ribs of suction cups made up of rods. 



f\ Ribs composed of 3 rods ; knob or hook lacking on anterior margin 

 of first antennae ; lobe of fourth leg boot-shaped, toe extending 

 to or beyond edge of abdomen; whole body circular; anterior 

 respiratory area minute, posterior very large — indicus (p. 552) 

 f. Ribs composed of 4 to 6 rods ; anterior hook present on first an- 

 tennae ; lobe of fourth leg large, semicircular, without a heel ; 



"Two species overlooked in making up this key are A. cubensis Wilson and A. rhamdiae 

 Wilson (cf. footnote p. 652.) 



