402 Wisconsin Academy of Sciences, Arts, and Letters. 



The following- description is taken from the Revision with- 

 ont any change : ' 



''Cephalothorax segmentis constans 7, quorum anterior^: duo 

 indistincte sejuncta caput componunt. Segmentum ultimiun 

 thoracale in femina sat niagnuni, postice in medio profundius 

 emarginatum adque latere saepius utrinque in laminam exiens 

 biangulatam. Abdomen breve thorace angustius, in femina 

 (ramis caudalibus inclusis) segmentis 4, quorimi 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 



1 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 tentaculi- 

 form appendages. The antennae of the first i>air 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, diiTerent from the others, are of five segments, with the 

 second segment arm on the inner side witlT 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. 



