84 Journal New York Entomological Society, [^'"i- xxix, 



elongate. The gnathofimbrium " gf " is well developed and is com- 

 posed of flattened seta-like processes. The lacinia mobilis "Ini" is 

 somewhat reduced, but is still of a different character from the seta- 

 like components of the gnathofimbrium " gf," although in the man- 

 dibles shown in Figs, i and 3, the lacinia mobilis " Im " does not 

 differ greatly from the structures composing the gnathofimbrium " gj." 



In the decapod shown in Fig. 6, the mandibular palpus has be- 

 come atrophied, and the beginning of the process is shown in the 

 decapod depicted in Fig. 35, in which the mandibular palpus '' en " 

 is merely a small rudimentary appendage of the greatly developed 

 mandible proper. The incisor process " in" of the decapod shown in 

 Fig. 6 is not very large, and it has completely disappeared in the 

 decapod shown in Fig. 26, which has retained only the molar process 

 " mo " of the distal structures of the mandible. The gnathofimbrium 

 and lacinia mobilis have apparently not developed in the decapod 

 types of Crustacea, though Mysis (Fig. 7) which resembles Thy- 

 sanopoda, Eupliausia, and other forms related to the Decapoda, has 

 acquired a lacinia mobilis " l)ii," and a primitive sort of gnatho- 

 fimbrium " gf." 



In the mandible of Sqnilla (Fig. 28) the palpus "en" is very 

 small, and the structure which I have interpreted as the molar process 

 " mo " is folded back in a peculiar fashion. The incisor region " in " 

 is continued basalward in a region which may be the precursor of the 

 gnathofimbrium of higher forms. At any rate, the incisor surface 

 is of greater extent than in the higher forms. 



In the mandibles shown in Figs. 25 and 32, there is a peculiar 

 gnathofimbrial lobe " gf," and the molar process " mo " has taken on 

 a peculiar form, and is somewhat folded around in a fashion sug- 

 gestive of the process which has been carried to an extreme in the 

 molar process "mo" of Fig. 28. Just above the base of the mandib- 

 ular palpus " en " in Fig. 25, is a small protuberance which is pro- 

 duced into two tooth-like processes just above the base of the cut-off 

 mandibular palpus in Fig. 32. These tooth-like processes may be 

 the precursors of the elongate incisor '" tusks " of the mandibles of 

 certain ephemerid nymphs, or a process of the region " in " of Fig. 4 

 forms the tusk-like process of the mandibles of ephemerid nymphs. 



The mandible of a male of Gnathia (Fig. 27) resembles the 



