648 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVII. 



Fig. 26. — Chitin skeleton of the proboscis in 

 argulrs versicolor. 



branous edge is quite wide, and is supported b}^ chitin ribs whose 

 construction is peculiar. The stiffened circle which serves as an 



attachment for the powerful 

 nuiscles of these niaxillipeds, as 

 well as the membranous edge, 

 is raised into knobs at equal in- 

 tervals around its circumfer- 

 ence (fig. 27). From each knob 

 a chain of four slightly oblong 

 chitin plates extends outward 

 to the edge of the membrane. 

 These are placed end to end and 

 diminish regularly in size, the 

 distal one being less than half as 

 large as the proximal. Each is 

 convex at the proximal and con- 

 cave at the distal end, the con- 

 vexity of one plate fitting into 

 the concavity of the one next 

 inside it. In the first and second 

 plates the concavity is eccen- 

 trically situated, but in the two 

 outer ones it is approximately symmetrical. The plates are arranged 

 end to end and do not quite touch one 

 another, but leave narrow open spaces 

 of membrane. Thus, while strengthen- 

 ing the membrane they still leave it very 

 flexible. 



Posterior maxillipeds {^g. 28). — These 

 are also large and well armed. The 

 joints diminish in size much more regu- 

 larly than those of americanus; the plate 

 on the basal joint is triangular, with 

 long, stout, and not very sharp teeth; 

 the papillated area is comparatively large and armed with strong setae. 



The anterior half of the 

 second joint and the entire 

 ventral surface of the re- 

 maining three joints are 

 covered with good-sized 

 papillae, each carrying a 

 toothed scale. These pap- 

 illated scales are similar to 

 those on mnericanus, and 

 consist of a hemispherical or hemiellipsoidal papilla, upon whose sum- 

 mit is borne the toothed scale. The latter is inclined at an angle of 10 



Fig. 27.^Chitix ribs ix the margin of 

 the sucking disks of argull's versi- 

 COLOR. 



0.5;;/ ;;;. 

 Fig. 28.— Posterior .maxilliped of argulus versicolor. 



