FREE-SWIMMING COPEPODS OF THE WOODS HOLE REGION. 
171 
the other plumes were present. There could he no mistaking the specific identity of my specimens. 
It is known to occur in the Mediterranean (Claus and Gieshrecht) and in the Pacific Ocean 108° to 
124° AY. and 0° to 11° N. (Gieshrecht). 
CLAUSOCALANUS Gieshrecht. 
Rostrum ending in two points ; terminal joint of anterior antennie fused with penultimate joint ; 
second and third pairs of feet with broad, calyculate basal joint, crenat.ed on its distal border, and 
also with broad outer rami. Mouth parts of male much reduced, as is also the number of joints in 
anterior antennae of the same sex. 
Female: Head fused with first thoracic segment, fourth with the fifth thoracic segment; rostrum 
with 2 short, rather stiff filaments. Abdomen with 
4 segments; genital segment and furca symmetrical. 
Anterior antenna.' reaching beyond thorax, 23-jointed, 
eighth joint fused with ninth, twenty-fourth with the 
twenty-fifth; aesthetasks short, bristles of terminal 
joint elongated. Outer ramus of posterior antennae 11 
times as long as inner ramus ; the former 6-joiuted, with 
short bristles on the proximal joints. First joint of 
inner ramus of mandible, with a very short, sac-shaped 
appendage. Maxillae and maxillipeds similar to those of 
Calanus; outer marginal bristle lacking in anterior 
maxilliped. Outer rami of third pair of feet, inner 
ramus of first pair 1-jointed, of second pair 2-jointed, 
of third and fourth pairs 3-jointed; terminal joint of 
outer ramus with finely denticulate terminal saw and 4 
inner marginal bristles on the second to fourth pairs. 
Fifth pair of feet short, consisting of 2 uniramous, 3- 
jointed feet. 
Male: Head and first thoracic segment fused, 
lengthened at expense of free thoracic rings; rostrum 
reduced; abdomen with 5 segments, of which the anal 
is very short. In anterior antenna', the first fuses with 
swollen second joint, the eighth to tenth, thirteenth to 
sixteenth, the twentieth and twenty-first; aesthetasks 
enlarged. Outer ramus of posterior antennae more than 
twice as long as inner ramus. Mandibular blade, ap- 
pendages of inner border of maxillae, and anterior 
maxilliped stunted; this is less the case with posterior 
maxilliped, the outer marginal bristles of which are not 
enlarged. Feet elongated. Left foot of fifth pair long, uniramous and 5-jointed, right foot short and 
1 to 3 jointed. 
9. Clausocalanus arcuicornis Dana. 
Female: Genital segment longer than third or fourth abdominal segment; furca about as long as 
broad. No msthetasks on joints 4, 6, 8, 18, 22 of anterior antennas. 
Male: Second abdominal segment as long as third and fourth segments together; right fifth foot 
3-jointed. 
Coloration: Not very transparent, with red pigment in some parts of thoracic segments, on dorsal 
and ventral surfaces and in genital segment. In male the pigment is on the whole more abundant and 
may extend into basal joints of anterior antennae. In rare instances all the chitinous cuticle has a 
violet color. The eggs are iose-colored. 
Length of female, 1.15 to 1.6 mm. ; of male, 1.12 to 1.2 mm. 
Three male and numerous female specimens were taken in the Gulf Stream July 29, 1899. The 
males all had the chitinous cuticle of a pale pellucid violet color. 
