FREE-SWIMMING COPEPODS OF THE WOODS HOLE REGION. 
187 
joint of mandibles with 2 hook-shaped bristles. Inner ramus of maxillae with a minute bristle. 
Outer ramus of first pair of feet with 1, 1, 2, of second and third with 1, 0, 1, of fourth with 0, 0, 0, 
outer marginal bristles. 
Male: Genital segment smaller than in O. plumifera. Proximal joint of distal portion of anterior 
antennas with a semicircular 2 irocess on inner margin. Third joint of outer ramus of first to fourth 
pairs of feet with 2 outer marginal bristles. 
Coloration: Similar to 0. plumifera, but usually less colored. 
Length of female, 0.73 to 0.8 mm. ; of male, 0.59 to 0.61 mm. 
This species occurred occasionally in small numbers in the tow taken from the Fish Commission 
wharf at Woods Hole during July, 1899. All the specimens were colorless. 
22. Githona plumifera Baird; 
female. 
23. Oithona similis Claus; a, male, dorsal aspect; 
b, female, dorsal aspect; c, male, anterior anteDna 
(dorsal surface) ; after Giesbrecht. 
Family HARFACTICIDJE. 
SETELLA Dana. 
Female: Trunk long and slender, laterally compressed. Cephalotliorax with 4 segments (head 
fused with first thoracic), abdomen with 5 segments (first and second segments fused) ; rostrum mova- 
ble; furca rod-shaped, with very long bristles. Anterior antenna} 8-jointed, with festhetasks on fourth 
and eighth joints. Posterior antenna} short, 2-jointed (basal fused with first joint of inner ramus), 
without a trace of an outer ramus. Succeeding 3 pairs of limbs minute; mandible 1-jointed, without 
rami, with denticulate blade ; maxilla also 1-jointed and without rami ; anterior maxilliped with 2 lobes 
and short terminal hooks. Posterior maxilliped longer and more powerful, 2-jointed, with terminal 
hooks. Feet with very long and slender rami; inner ramus of first pair 2-jointed; remaining rami 
3-joiuted; fifth pair of feet rudimental, elongate leaf-shaped. 
Male: With separate first and second abdominal segments; grasping antennae 8-jointed, with 
articulation between fifth and sixth joint; fifth pair of feet similar to those of the female, but 
Smaller, with weaker bristles; sexual differences also in first and especially in second pair of feet. 
