74 Journal Xew York Entomological Society. [^'°1- >^xiX; 



of textfigure 3. The black margined area from " a " to " c " be- 

 comes proportionately longer, and arches over in such a fashion that 

 the point of attachment from " a " to " h " instead of being more 

 horizontal as in textfigures 2 and i, tends to become more vertical 

 (or obliquely so) in the mandibular appendage shown in textfigure 3. 



If there were any question as to whether the palpus " en " of 

 textfigure 3 (compare also Fig. 10, Plate VII) represents the endo- 

 podite or the exopodite of a biramous limb, a glance at Fig. 33 

 (Plate VIII) will readily convince anyone that the exopodite "ex" 

 becomes reduced and is eventually lost, while the endopodite is re- 

 tained to form the palpus when the palpus is present. The mandibles 

 shown in Figs. 30 and 33 (Plate VIII) would doubtless have fur- 

 nished better intermediate stages than the merostome limb used in 

 textfigure 2 to illustrate the transition from the type shown in text- 

 figure I to that shown in textfigure 3, and these forms stand more 

 nearly in the direct line of descent of the higher Crustacea; but there 

 are certain features which the merostome limb illustrates better 

 than these other forms, and the figure of a merostome limb serves 

 well enough for the purpose intended. 



Since there is only what appears to be a molar area "mo" in the 

 mandible of the branchiopod Branchippius shown in Fig. 23 (Plate 

 VIII), this suggests that the molar area " )iio" of Fig. 23 may repre- 

 sent the entire " masticatory " area of the mandible of Apiis, shown 

 in Fig. 22. I am more inclined, however, to think that the region 

 labeled " in" in Fig. 22 corresponds to the incisor area " in " of Fig. 

 10 (Plate VI) while the closely packed processes "mo" of Fig. 22 

 (Plate VIII) in the proximal portion of the masticatory area, may 

 form the molar area "mo" of Figs. 10 and 23. In this connection, 

 it should be noted that the mandible of Apus assumes the position 

 shown in Fig. 24 when " in situ" and consequently it must be turned 

 over and placed in an upright position as in Fig. 22, if it is to be 

 compared with the mandibles of other forms, which have assumed 

 the latter position. The fact that the molar process " mo " is the 

 only portion of the masticatory area preserved in the shrimp shown 

 in Fig. 26 (Plate VIII) makes it more readily comprehensible that 

 the molar area might be the only portion of the masticatory area 

 preserved in the branchiopod shown in Fig. 23 ; but I would not insist 



