182 University of California Publications. [ ZooLoGy 
tenna usually the left; first and second joints fused, as well as 
the nineteenth to twenty-first, twenty-second and twenty-third 
(or twenty-second to twenty-fifth) ; fifth pair of feet with 3- 
jointed outer and 1- to 3-jointed inner ramus; forceps incomplete 
or absent. 
1. Genus Heterorhabdus Giesbrecht. 
Heterochaeta Claus, 1863, p. 180. 
Heterochaeta Brady, 1883, p. 48. 
Heterochaeta Giesbrecht, 1892, pp. 64, 372, 745; 1895, p. 259. 
Heterochaeta, Aurivillius, 1899, p. 38, figs. 4, 5. 
Heterorhabdus Giesbrecht, 1898, p. 113. 
Heterorhabdus Wolfenden, 1904, p. 124. 
2 Cephalothorax with five segments, rostral filaments soft, 
situated on a papilla. Abdomen with four segments, left half of 
furea not articulating with anal segment, larger than the right 
and with much longer bristles. Rami of posterior antennae about 
equal in length, outer ramus with eight bristles. Anterior maxil- 
liped straight, terminal portion and proximal lobes with their 
bristles strongly suppressed, while the distal lobes are provided 
with strong hooked bristles. Posterior maxillipeds distinguished 
by shortness of the bristles on the inner ramus and by the length 
and thickness of one bristle on the inner margin of the first basal 
joint. All the feet have 3-jointed rami; inner marginal bristle 
of the first basal in pairs one to four, and of the distal basal joint 
in the first pair, well-developed and plumose. Terminal joint 
of outer ramus of third pair usually different in form from that 
joint in the other pairs, being broad and oval (fig. 38d). The 
inner marginal bristle of the second joint of the outer ramus of 
the fifth pair is thickened and sword-shaped (fig. 38e). 
4 Sexual peculiarities in form of posterior portion of body, 
left anterior antenna and fifth pair of feet. Abdomen with five 
segments, genital opening on right side. Grasping antenna 
slender. Fifth pair of feet with 3-jointed rami; terminal joints 
of both outer rami hooked; processes on the distal basal joint. 
KEY TO SPECIES. 
Abdomen 4-segmented, fifth foot symmetrical.................- 2 
Abdomen 5-segmented, fifth foot asymmetrical................ 5 
-1. Third joint of outer ramus of third foot of same form as in 
second and fourth pairs) (fies 400). ar etait H. longicornis 
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