1894,] The Classification of the Arthropoda. 133 
hardly more doubtful is the view which would compare the 
Phyllopod appendage with the Annelid parapodium. But two- 
and three-branched appendages are not unknown outside the 
Crustacea. One of the arguments advanced in favor of a Crus- 
tacean position for Limulus is that the abdominal appendages 
in that form are two-branched, while numerous observers have 
recorded a biramous condition in the appendages of the 
young of various “ Tracheates.” Among others we would men- 
tion the biramous pedipalps in Dendryphantes recorded by 
Croneberg (’80), the biflagellate antenna of an Indian Lepisma, 
and ofan embryo Blatta javanica by Wood-Mason (’79), the bifid 
condition of the antenna of Blatta by Wheeler (’89), while 
Patten (’84), in the same form, describes the maxille and 
labium as “ formed respectively of two and three branches, the 
second maxille thus attaining the typical trichotomous struc- 
ture of the Crustacean appendages.” Similar observations 
have been made upon other Hexapods, while in the Pauropida 
the trichotomous antennz are to be called to mind. 
. Fully as characteristic is the extreme reduction of the ento- 
dermal portion of the alimentary canal proper, the entoderm 
cells being largely confined to the liver or mid-gut gland, 
while the canal itself is almost entirely composed of stomodeal 
and proctodeal invaginations (cf Kingsley, ’89, pp. 18-19). 
Sus-CLiass I—TRILOBITÆ OR Patmocaripa? 
Fossil Crustacea with tri-regional body—head, thorax, pygid- 
ium, all bearing appendages. “ Head ” unsegmented, with one 
pair of antennz and with four pairs of postoral appendages, 
all pediform and with basal points manducatory. Thoracic 
somites indefinite in number, each bearing a pair of biramous 
(exopodite and endopodite) appendages, each appendage pro- 
vided with a straight or curiously coiled gill (?). Pygidium 
Segmented, with appendages beneath. 
For several years I have maintained that the Trilobites had but 
the most distant affinities with the Xiph (e. g., ’85, p. 555). - 
$ This term was introduced by Packard (’79) for Limulus, the Trilobites and the 
Eurypterids. Later (’86), with no apparent reason, he dropped this term and substi- 
tuted for it Podostomata. The two groups, as he limits them, are exactly the same. 
