75 



and in the 2-segTnented abdomen and proportions of tlie furca, 

 wliile it differs from that species in the presence of rather long 

 hooks to the rostrum, in the shorter antennae and in the absence 

 of the plumose setae to the outer margins of the basal segments 

 of the 5th feet. It also differs from L. aestiva in the last thoracic 

 segment being not so sharply pointed at the angles and in its 

 greater size (2.60mm as against 1.75mm to 2mm for L. aestiva.) 



The absence of the male form makes it difficult to settle defi- 

 nitely whether it is distinct from either of the two mentioned 

 species or merely a variety of one of them, and although the 

 above variations would almost warrant the erection of a new 

 species, the writer would prefer to leave that question open until 

 a closer examination of the preserved material is made. 



The minor points noticed were the densely hirsute margins 

 of joints I to 13 of the anterior antennae, some of the aesthetasks 

 and all the antennal setae being plumose, while on the proximal 

 setae the plumes were exceptionally well defined. The genital 

 segment has lateral hairs. The thorax of an average specimen 

 measured 2.04mm; abdomen, .56mm. Genital segment as 14:8 

 in proportion to the foUow-segment ; 2d segment to furca as 

 107; length of furca to width as 7:3; length of furcal setae, 

 .39mm. 



8. Acartia tonsa Dana. 



9. Acartia gracilis Herrick 



Herrick ('84, p. 181) noted with doubt a form from the Gulf 

 under the name of Dias longiremis Lilljeborg. His material was 

 insufficient to establish his diagnosis definitely, and while he sub- 

 sequently ('87, p. 7; pi. I, figs I, la and 2) recorded and figured 

 the same species under Acartia gracilis, and at the same time gave 

 a short desription and comparison with other species of the genus, 

 his diagnosis is so incomplete as to be relatively of very little 

 value to the student of the Copepoda. Moreover, his figure of the 

 female animal itself gives 20 joints to the anterior antennae, 

 whereas only 17 are present in Acartia. For this error he may 

 be excused through the paucity of material and the fact that the 

 joints are extremely difficult to differentiate both in the live 

 animal and in preserved specimens. 



Giesbrecht and Schmeil ('98, p. 156) record merely the name 

 and place it among their uncertain species. 



The overwhelming predominence of this form at all stations, 

 and the fact that it is quite the commonest species in the Gulf, 

 off Pass Christian and in Lake Pontchartrain lead the writer tO: 

 believe that the species has once more come under observation. 



