1(34 
BULLETIN OF THE UNITED STATES- FISH COMMISSION. 
Lateral corners of last thoracic segment each prolonged into a long-pointed process; outer 
ramus of first foot 3-jointed FI? 
Lateral corners of last thoracic segment rounded, sometimes slightly pointed; outer ramus of 
first foot 2-jointed F 2 ? 
Rostrum ending in 2 stout, strongly chitinized prongs; rami of posterior antennae of about 
same length Aetidius 
Rostrum wanting ; innerramus of posterior antennae about half as long as outer ramus . Chiridius. 
Rami of posterior antennae of about the same length Euchata 
Outer ramus of posterior antennae at least If times as long as inner ramus F 3? 
Inner border of first basal joint of fourth foot naked or with a few small hairs ; median bristles 
of outer ramus of maxillae shorter than the proximal and distal bristles Undeuchrvta 
Inner border of first basal joint of fourth foot with spinose or crenate bristles ; median bristles of 
outer ramus of maxillm not abbreviated Euchirella 
Only one foot of the fifth pair present and this is uniramous ; lateral portions of last thoracic 
segment pointed Aetidius $ 
Feet of fifth pair both powerfully developed; lateral portions of the last thoracic segment 
rounded F 1 
Inner ramus of posterior antenna considerably shorter than outer ramus; right fifth foot 
chelate Euchirella $ 
Rami of posterior antennae about same length; fifth foot not chelate, the right, sometimes also 
the left, hearing a stylet-shaped appendage Euclueta. 
Suborder GYMNOPLEA. 
Family CALANIDiE. 
CALANUS Leach. 
Female: Head free or fused with first thoracic segment; fifth thoracic segment free, sometimes 
asymmetrical; rostrum ending in two points; abdomen composed of 4 segments; genital segment 
symmetrical; furca occasionally slightly asymmetrical. Anterior antenna) sometimes not reaching 
hind end of body, sometimes extending a considerable distance beyond, and not always of symmetrical 
length, 25-jointed, with very uniformly distributed short antero-marginal bristles and delicate 
sesthetasks, and 2 long and plumose postero-marginal set® on terminal joints. Rami of posterior 
antenn® of about equal length, outer ramus 7-jointed. Mandibular blade with 8 rather flat teeth; 
rami of about equal length, proximal joint of inner ramus with sack-shaped appendage. Maxillae 
with 3-jointed inner ramus, articulating with basal; outer lobe with bristle. Anterior maxilliped 
relatively long, with long curved bristles on inner and a plumose bristle on outer margin. Posterior 
maxilliped with long 5-jointed inner ramus, provided with long, stiff, usually naked bristles. 
Male: Abdomen composed of 5 segments; genital orifice sinistral; furcal bristles abbreviated. 
Anterior antennae held in an unusual position and sometimes abbreviated, the number of their joints 
reduced (at least the first two joints fused), twenty-fifth joint usually abbreviated, aesthetasks 
enlarged and increased in number, bristles, with rare exceptions, reduced. Posterior antennae stouter 
than in female, with in part abbreviated bristles; outer ramus with an S-shaped curvature. Mandib- 
ular blade weaker and in some species stunted; in these same forms the inner marginal appendages of 
maxillae and of the anterior maxillipeds are decidedly stunted. In general a stronger development of 
outer marginal bristles at end of posterior maxilliped, which in some species are also stunted, owing 
to shortening, obliteration of joints, and absence of bristles. In some species differences as compared 
with the femaile are found also in separation of head from first thoracic segment, in form of lastthoracic 
segment, and in the feet. 
1. Calanus finmarchicus Gunner. 
Female: Head separated from first thoracic segment; front and lateral portions of fifth thoracic 
segment rounded; furcal bristles symmetrical. Anterior antenn® reaching about to end of trunk; 
®sthetasks not duplicated on any joints. Distal margin of second basal joint of second to fourth 
pairs of legs with pointed projection; ratio of lengths of portions of outer margins of third joint 
of outer ramus in second to fourth pairs as 2:1; 2:1; 3:1. First basal of fifth pair with concave, 
denticulated inner border. 
Male: Head separated from first thoracic segment. Anterior antenn® straight (joints 1 and 2 
fused) . Mouth parts similar to those of female (outer bristle of fourth joint of inner ramus of posterior 
F $ . 
FIS. 
F 2 ? . 
F 3?. 
F $ . 
F 1 S . 
