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2 University of California PuMications in Zoology [Vol. 13 



as "the first thoracic limb" and of its endopodite as "the first leg," 

 and so on. These authors refer to eight legs (endopodites) while 

 Zimmer uses the term cormopod in the sense in which they use thoracic 

 limb. Sars speaks of the maxilliped and the legs, separately. 



Hansen (1909, p. 6) in his discussion of the Mysidacea applies 

 the term gnathopod to the appendage which, according to Zimmer, is 

 the second cormopod, according to Holt and Tattersall the second 

 thoracic leg, and in Sars's terminology the first leg. It is probable 

 that Hansen intends his designation to hold for the Mysidacea only, 

 though he does not say so. 



It is plain that among the Euphausiacea there are eight pairs of 

 legs so far as the use of the organs is concerned and disregarding the 

 possible relationships of the appendages in comparison with other 

 Crustacea. For that reason, it seems to me that the usage of Holt and 

 Tattersall is distinctly advantageous. The cormopods are not used 

 as feeding organs but as walking legs ("Gangfiisse," Zimmer, 1909, 

 p. 3), and though the last two pairs are apt to be more or less re- 

 duced, the use of the term leg is advisable for general purposes. The 

 suggestion of Holt and Tattersall as to numbering the limbs is fol- 

 lowed in this paper. 



The appendages of the abdomen with the exception of those on 

 the sixth segment may properly be called pleopods in most cases, 

 and no confusion can arise from the use of that term. The last seg- 

 ment of the abdomen is the telson, and the two broad plates on each 

 side of it are the uropods which are always biramous. The telson 

 and the two pairs of uropods make up the tail fin or caudal fan. 



Sars (1885, p. 5) gives a detailed account of the general morph- 

 ology of the Schizopoda, and useful discussions will be found in Ort- 

 mann (1893, p. 3) and Zimmer (1909, p. 1). 



Most authors consider that the Schizopoda are separable into two 

 orders, the Euphausiacea and the Mysidacea. Sars (1885, p. 10) 

 divided the Schizopods into four families, but it appears that sub- 

 sequent writers have not followed this arrangement. It is now gen- 

 erally agreed that the order Euphausiacea includes one family, 

 Euphausiidae, to which the more highly organized Schizopoda belong. 

 A brief diagnosis of the family is as follows. There are two rather 

 easily determined points: first, the legs have gills attached to them 

 and the gills are not covered over by the sides of the carapace ; second, 

 the telson carries on each side a subapical spine or "lancet" located a 

 short distance anterior to the tip (pi. 2, fig. 27). The side margin 



