144 University of California Publications. [ ZOOLOGY 
abdomen invariably. Rostrum strongly chitinized, usually with 
one point, seldom with two or lacking. Genital segment and 
furea usually symmetrical. In the anterior antennae the eighth 
and ninth and twenty-fourth and twenty-fifth joints are fused. 
Outer ramus of posterior antennae at least fully as long as the 
inner, and usually longer; the second and third joints of the. 
outer ramus are distinct. Mandible as in Calanus, with strong 
blade, and occasionally shortened inner ramus. Maxilla with 
well developed lobes on inner margin and usually with hooked 
bristles even on the second basal and the inner ramus; outer 
ramus relatively small. Bristles of anterior maxilliped short but 
strong, those of the inner ramus relatively slender and sparsely 
plumose; the articulation of the inner ramus is rather on the 
_ posterior surface of the second basal than at the end. Inner 
ramus of posterior maxillipeds at most 24 as long as the second 
basal. Inner ramus of first swimming feet always 1-jointed; that 
of the second almost always 1-jointed, while in the second and 
third the inner ramus is 3-jointed; the form of the swimming 
feet as in the Clausocalaninae; inner marginal bristle of first 
basal long and plumose. 
4 Known in Aetideus, Euchirella and Undeuchaeta. Charac- 
ters like those of Clausocalanus; oceasionally the twentieth 
and twenty-first joints of one of the anterior antennae are fused. 
Left foot of fifth pair 5-jointed (if the right is lacking, or stylet- 
like, in which ease the right is claw-like). 
1. Genus Aetideus Brady. 
Aetidius Brady, 1883, p. 75. 
Aetidius Thompson, 1888b, p. 142. 
Aetidius Giesbrecht, 1892, pp. 53, 213. 
Aetideus Wolfenden, 1903, p. 266; 1904, p. 116. 
Aetideus Giesbrecht, 1898, p. 31. 
2 Cephalothorax and abdomen with four segments, symmet- 
rical; rostrum large, prolonged into two thick chitinous prongs; 
last thoracic segment produced into a spine on each side. Ante- 
rior antennae 23-jointed, reaching about to the end of body. Rami 
of posterior antennae about equal in length, outer ramus 7- 
jointed. Outer rami of all swimming feet 3-jointed, inner ramus 
of first and second pairs 1-jointed, of third and fourth 3-jointed. 
Fifth pair of feet absent. 
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