AMERICAN PARASITIC ARG ULIDM- WILSON. 699 



In lepidostelihQ basal joint of the second leg's projects posteriorly as 

 an enormous flap, and there is a rounded knob on the anterior surface 

 of the distal basipod joint of the third leg-s similar to that in vernlcolor 

 (Plate XVI). 



In macidosus there is a more plentiful suppl}^ of projections and 

 knobs; projections posteriorly at the outer ends of the basipods of the 

 third leg's and of the basal joint of the second legs, and an anterior 

 projection at the outer end of the basal joint of the third legs; knobs 

 on the posterior surface of the distal basipod joint of the fourth legs, 

 on the anterior surfaces of both joints of the third legs and the same 

 surface of the basal joint of the second legs (Plate XIX). 



But it is in americanus that the projections reach the maximum for 

 any species so far examined. Here at the outer end of the basal joint 

 of the third legs on its anterior surface arises a long club-shaped pro- 

 jection which reaches past the distal basipod joint and extends far out 

 on the exopod. 



There is another conical projection, oniy slightly smaller, exactly 

 opposite on the posterior surface of the preceding pair of legs. Both 

 projections are profusely covered with seta^. There are also smaller 

 projections on the opposite surfaces of the same joints as bear the large 

 ones (Plate XXI). 



SYSTEMATIC. 



The Argulidoe were classed by Kroyer with the Siphonostoma, but 

 Zenker in 1854 withdrew them from this group in consequence of a 

 mistaken interpretation of the mouth parts. 



Later Thorell placed the Argulida? as a third suborder of the Bran- 

 chiopoda, of equal value with the Phyllopods and Cladocera, giving as 

 his particular reasons the unfacetted cornea of the compound eyes, the 

 absence of palps or branchial appendages on the oral organs, the 

 absence of external egg- sacs and spermatophores, and the funda- 

 mental form of their extremities. 



But Claus in 1875 showed very clearly that the Argulida are much 

 more closely related to the Eucopepoda than to the Branchiopods, and 

 while retaining the name Branchiura given them l)y Thorell, he places 

 them under the Copepoda as a second su})order oi 0([ual value with the 

 Eucopepods 



That Claus i.s right and that the Argulida are much more closely 

 related to the Eucopepods than to the Phyllopods has been clearly 

 shown in the preceding ontogeny and morphology in the following 

 points: 



1. They have a flattened body which shows exactly the same general 

 form as in the less degenerate Siphonostoma (Caligidtv, etc.), the same 

 division into regions, and the same segmentation, part for part. The 

 head is fused with the lirst thoracic segment, while the other thoracic 



