402 Wisconsin Academy of Sciences, Arts, and Letters. 
The following description is taken from the Revision with¬ 
out any change: 1 
“Cephalothorax segmentis const ans 7, quorum anterior a duo 
indistincte sejuncta caput componunt. Segmentum ultimum 
thoracale in femina sat magnum, postice in medio profundius 
emarginatum adque latera saepius utrinque in laminam exiens 
biangulatam. Abdomen breve thorace angustius, in femina 
(ramis caudalibus inclusis) segmentis 4, quorum primum in 
parte antica dilatatum saepiusque utrinque mucrone laterali 
armatum est; in mare vero segmentis 6 ejusdem fere latitudi- 
nis compositum. Rami caudales setis 5 uniarticulatis et plu- 
mosis, setaque alia multo tenuiore intus adfixa praediti. Frons 
i The following translation of the original account of the genus 
Diaptomus may be given: 
Cephalothorax always of seven segments, of which the two anterior, 
indistinctly separated, form the head. The last thoracic segment in 
the female is rather large, posteriorly in the middle rather deeply 
emarginate, and quite frequently produced laterally on both sides 
into a biangulate lamina. Abdomen short, narrower than the thorax, 
in the female, including the caudal rami, of four segments, of which, 
the first is dilated anteriorly, and commonly armed with a lateral 
spine on each side; but in the male it is composed of six segments of 
nearly equal width. The caudal rami are armed with five uniarticulate 
plumose setae, and with another much more slender seta attached on 
the inner side. The front is provided with two very minute tentacull- 
form appendages. The antennae of the first pair are composed of 
twenty-five segments, which increase a little in length toward the tip; 
the right antenna of the male is geniculate with the articulation be¬ 
tween the eighteenth and nineteenth segments; the six preceding are 
swollen, and the five following more or less united into two segments. 
The outer ramus of the second pair of antennae is longer than the in- 
ner, composed of seven segments, the last segment longest of all and 
armed with very long apical setae; the setae attached to the preced¬ 
ing segments are short and nearly equal. The second pair of maxillae 
are short and thick; the third pair are elongate, turned forward, of 
seven segments, and furnished with short setae. The eight anterior 
swimming feet are biramose, the inner ramus of the first pair of two 
segments, and of the following pairs of three segments; the feet of the 
last pair, different from the others, are of five segments, with the 
second segment arm on the inner side with" a small attendate for 
rudiment of an inner ramus; in the female they are short, equal to 
each other, the last segment very short and rudimentary, the penulti¬ 
mate always produced into a strong hook, curved inward; the right 
foot of the male is subcheliform, with the last segment formed into a 
very long movable hook. The eye is single. 
