44 K 



Canadian Arctic Expedition, 1913-18 



which may represent a rudimentary (i.e., vestigial) labrum. In front of this 

 there is another median papilla of uncertain significance, and before this again 

 a pair of clear oval areas. At the base of each anterior antenna there is a small 

 transversely elongate chitinous thickening. Finally, on either side of the 

 supposed labrum there is a wrinkled papilla showing a small central cavity; 

 these are the possible vestiges of posterior antennae (Fig. 69). 



Fig. 69. T. bernardensis. Ventral side of head. 



The five antennary joints have the numerical proportions 8, 10, 5, 15, 16. 

 The fifth joint carries a strong, terminal claw-like seta, which can be held for- 

 wards or bent at a right angle to the joint. The following setae are to be found 

 at different points on the antennae : 



First joint: a subulate seta with short plumes. 



Second joint: five shortly plumose subulate setae, of which three are to be 

 seen at the margin (Fig. 69), and in addition a long plumose seta arising dor- 

 sally at the distal margin, whose long plumes occur on the slender distal portion 

 of it. 



Third joint: two long plumose setae and a shorter subulate seta beset with 

 fine points. 



Fourth joint: sever, setae, including a slender aesthetask or sensory filament 

 and one long plumose seta: proximad of the long plumose seta are two marginal 

 subulate setae of which the proximal one is the longer; removed from the mar- 

 gin a little in front of the proximal subulate seta and proximad of the base of 

 the long seta is the aesthetask. In Th. longispinosus, Giesbrecht figures the 

 aesthetask alongside of the long seta. Distal to the base of the long seta is a 

 marginal subulate seta like the proximal one. Exactly opposite the base of 

 the long seta is a short subulate seta, and in front of this a precisely similar 

 one. In Giesbrecht's figure of Th. longispinosus, in place of the single marginal 

 proximal subulate seta, there are two equal setae side by side. 



Fifth joint (Fig. 70) : there are three branched setae, a long plumose seta, 

 four soft slender setae which look like aesthetasks, a marginal and a subterminal 

 subulate seta and the terminal claw, making eleven altogether, as in Th. longi- 

 spinosus. 



The swimming feet are all alike, both rami three-jointed, the Re with 

 1. 0, 1 se; 1, 1, 4 si; and one st. The st is plumose, like the others. The Ri 

 has 1, 1, 5 setae. The se of B2 is quite small and slender, longer on the third 



