70 Journal New York Entomological Society. tVoi. xxix, 



" swimming " leg) like, I would refer to the appendages in question 

 in the trilobite as protantennse, protomandibles, protomaxillul?e and 

 protomaxillae, to indicate that they are the precursors of the second 

 antennae, mandibles, maxillul?e (first maxill?e) and maxill^E (second) 

 of Crustacea, but have not yet become sufficiently modified to take 

 on the form of these structures exhibited by the Crustacea, although 

 the first antennse (antennulse) of trilobites have lost the walking-leg 

 form and have taken on the character of true antennae. 



I have been astonished to find that in such ancient and apparently 

 primitive Crustacea as Apiis (Fig. 22) and Branchippus (Fig. 23) the 

 mandibles have lost their original limb-like character and have as- 

 sumed the form of true mandibular jaws. Even in the Copepoda 

 (Fig. 30) and Ostracoda (Fig. 33) the mandibular appendages have 

 become so far modified that the terminal portion of the mandibular 

 limb has taken on the appearance of a palpus of the basal segment 

 which forms the body of the mandible proper, despite the fact that 

 the terminal portion of the mandibular limb {i.e., the palpus) in these 

 forms has still retained the inner branch "en" and outer branch 

 "ex" of the primitive biramous crustacean and trilobitan limb (com- 

 pare with textfigures i and 8, "en" and "ex"). On the other hand, 

 the mandibular appendage (protomandible) of trilobites is almost 

 exactly like a " walking "' leg, and in the Merostomata, Pantopoda, 

 Scorpionida, and the arachnoids in general, the appendage homo- 

 logous with the mandibles of insects, myriopods, and Crustacea is 

 more like a limb than it is like a jaw. I would therefore divide the 

 arthropods into two subphyla, one of which the Eiigiiathata contains 

 the Insecta, " Myriopoda," and Crustacea, and is characterized by 

 the modification of the mandibular appendage to form a true mandible 

 (with terminal segments either lost, or reduced to form a palpus) ; 

 while the other subphylum, the Podognathata, contains the remainder 

 of the arthropods, in which the mandibular appendage is essentially 

 like a limb, the terminal segments being of such a character that they 

 do not form a mere palpus-like organ for the basal jaw segment. 



Such a division of the arthropods would group the trilobites with 

 the IMerostomata somewhat more closely than with the Crustacea, 

 and such a grouping would be justified by the character of the head 

 (which is flattened with the eyes located above), by the character of 



