June, 1921.] CraMI'TOX: EvOLUTIOX of the AxTHROrODA. 89 



by Boas, 1882. Caiman and otlier recent carcinoloj^ists liave removed 

 the Mysidacea from the old order Schizopoda which also included the 

 Euphausiacea, etc., and have grouped the Mysidacea with the 

 Cumacea. Tanaidacca, Isopoda, etc., because of the presence of the 

 lacinia mobilis (among other features) in these forms and its absence 

 in the Euphausiacea and Decapoda. I cannot avoid the conclusion 

 that the Mysidacea are much nearer the Euphausiacea. however, de- 

 spite these facts, although the Mysidacea are evidently intermediate 

 between the Euphausiacea on the one side, and the Cumacea, Tanai- 

 dacea, Isopoda, etc., on the other. It is thus a matter of determining 

 the closest atfinities of tlie Mysidacea and not a question of their 

 intermediate character, which is to be decided; and while the evidence 

 of the mandil)les would support the view that the Mysidacea are 

 somewhat nearer the Cumacea, Tanaidacea, etc., I am by no means 

 satisfied that other points of resemblance between the Mysidacea and 

 Eui^hausiacea are not of greater importance. 



The mandibles of the Syncarida such as Aiiaspidcs have no lacinia 

 mobilis; but a gnathofimbrial lobe very suggestive of that shown in 

 Fig. 25, " gf," occurs on the mandil)le of Anaspidcs, and. contrary 

 to the opinion of Caiman. I would maintain that the Syncarida are 

 nearer the types ancestral to the Tanaidacea. Isopoda, etc., than they 

 are accredited to be by Caiman and other carcinologists. In fact, it is 

 quite probable that the common ancestors of the Tanaidacea, Iso- 

 poda, Amphipoda, Insecta and Syniphyla, etc., were anatomically 

 intermediate between the Syncardia on the one side, and the Mysi- 

 dacea on the other and were related to the Arthropleura and Oxyuro- 

 poda as well ; but this matter will be discussed more at length in a 

 later paper. 



The mandible of a cumacean such as Diastylk ( I""ig. 2) bears a 

 well developed gnathofimbrium " gf " and a lacinia mobilis " Im," 

 and in the development of its incisor process, it resembles Apscudcs 

 (!''&• 3)- The Cumacea are regarded by Caiman as intermediate 

 between the Mysidacea and the isopod type of higher Crustacea, and 

 a study of tlie mandible would lend weight to this view. On the 

 other hand, the Cumacea are such highly aberrant forms, that they do 

 not furnish any very valuable clews as to the phylogeny of the 

 higher Crustacea. Their type of mandible, however, is as near that 



