142 University of California Publications. [ ZOOLOGY 
1. Genus Clausocalanus Giesbrecht. 
Calanus Dana, 1849, p. 278; 1852, p. 1047. 
Calanus Claus, 18638, p. 172. 
Eucalanus Claus, 1881, p. 325. 
Drepanopus (in part) Brady, 1883, p. 76. 
Clausocalanus Giesbrecht, 1888, p. 334; 1892, pp. 50, 185, 733; 
1898, p. 27. 
Rostrum with two points; second basal of second and third 
swimming feet with toothed distal margin and broad outer ramus. 
Mouth parts and number of segments of anterior antennae 
reduced. 
2 Head fused with thorax and the fourth with the fifth 
thoracic segment. Abdomen with four segments, genital segment 
and furca symmetrical. Anterior antennae extend beyond the 
thorax, 23-jointed. Outer ramus of posterior antennae 114 times 
as long as the inner, the former 6-jointed, with short bristles on 
the proximal joints. First joint of inner ramus of mandible 
with a very small, sack-like appendage. Maxilla and maxillipeds 
as in Calanus, outer marginal bristle lacking on anterior maxilli- 
peds. Outer rami of swimming feet with 3 joints; inner ramus 
of first foot 1-jointed, of second 2-jointed, of third and fourth 
3-jointed. End joint of outer ramus with finely dentate terminal 
bristle, and four bristles on inner border in second to fourth 
pairs; fifth pair uniramous, 3-jointed. 
4 Head fused with first thoracic segment, and elongated at 
expense of free thorax rings. Rostrum suppressed ; abdomen with 
five segments, anal very short. Anterior antennae with joints 
8-10, 13-16, 20-21, 24-25 fused. Outer ramus of posterior antennae 
twice as long as inner. Blade of mandible, appendage of inner 
border of maxilla, and anterior maxilliped suppressed ; less so the 
posterior maxilliped, the outer marginal bristle of which is not 
enlarged. Swimming feet elongated. Left fifth foot (fig. 13c) 
long, uniramous and with 5 joints, right short, 1- to 3-jointed. 
1. Clausocalanus arcuicornis Dana. 
Calanus arcuicornis Dana, 1849, p. 278; 1852, p. 1056; 1855, 
pl. 72, fig. 9a-b. 
Calanus mastigophorus Claus, 1863, p. 173, pl. 27, figs. 5-8. 
