366 CLASS CRUSTACEA. 



presence of a testa, in the form of an oval or semi-lunar 

 buckler; by the number of visible feet, which is always 

 twelve (or fourteen, if, with Dr. Leach, those may be considered 

 as such, which I think to be the two inferior antennae) ; by 

 the form and size of those of the last ten pair, which are 

 sometimes multifid, pinnate, or terminated in a fin, and very 

 weW adapted at all periods, and in the adult state, for 

 swimming ; sometimes in the form of leaflets, or broad and 

 membranaceous. The sides of the thorax never present ex- 

 pansions in the form of wings, inclining backwards, and they 

 enclose the body posteriorly. 



In some the body, presenting several segments above, is 

 elongated, and naiTOwed posteriorly, to terminate in the manner 

 of a tail with two filaments, or two other projecting append- 

 ages at the end. This extremity is not covered by a division of 

 the superior teguments, in the form of a large rounded shell 

 deeply notched at the posterior edge ; the testa occupies at 

 least one half of the length of the body ; this subdivision 

 will comprehend two genera of Mliller. 



The first, that of 



Ar G u L u s , Midler, 



Was at first designated by us under the name of Ozole, and 

 described in an incomplete manner. The younger Jurine has 

 since observed the species which serves as its type, with the 

 most scrupulous attention, has traced it in all its ages, and 

 given us a monograph which leaves nothing to desire 

 upon the subject. He has restored to this genus the name 

 which Mliller had originally imposed upon it. 



The arguli have an oval buckler, emarginated posteriorly, 

 covering the body, with the exception of the posterior ex- 

 tremity of the abdomen, supporting on a middle triangular 

 space, distinguished under the name of hood, (chaperon) two 

 eyes, four very small antennae, almost cylindrical, placed in 

 front, the superior of which, shorter and of three articulations. 



