372 



GEOLOGICAL SUEVEY OF THE TERRITORIES. 



appendages in general protopoda^ the term "cephalopoda" being other- 

 wise in use. The thorax of insects and of most of the Crustacea might 

 be designated the Bccnosome [fiar^o, to walk, locomotion), and the tho- 

 racic appendages Bceiiopoda, the segments being called hmnomeres ; 

 while Uroxome might be applied to the abdomen, the abdominal segments 

 being called uromeres. Westwood's term uropoda miglit be extended so 

 as to include all the abdominal appendages. The term gonopoda we 

 have suggested for the external organs of the Decapods concerned in 

 reproduction, which are simply modified uropoda. The long, slender, 

 antenna-like anal appendages of the cockroach, mantis, &c., correspond- 

 ing to the anal cerci of Acrydii, may be designated as cercopoda, and 

 this term might be applied to the terminal pair of uropoda of the Phyl- 

 lopods, i. <?., the jointed, slender, sjnnulose a])pendages of Apodidw, or 

 the unjointed appendages of the Branchlpodida^. 



The segments of the body. — The Phyllopoda are exceptional to other 

 Crustacea in having an indefinite number of segments composing the 

 body, and in having in one family {Apodidw) more than one pair of ap- 

 pendages to an arthromere. While the normal number in the Decapoda 

 is 20, in the Phyllopods it varies from 14 in Limnetis to 47 in Apus. The 

 following table shows the number in different genera of American si^e- 

 cies: 



M 









A 



SB 





4) 







to 



§ 



m 





^ 03 



02 





ri 





"ctf 'i. 







3 



i 



S' 



8) 



CD 



1- 



fl 





i 





^ 



a 







< 



^ 



3 



% 



'A 



<1 



H 



2 





1 





12 (-14) 







1 



2 





2 





23-27. 







1 



2 





2 





1 22 







1 



*2 





1 



fl 



27 (60 pairs 

 limbs). 



32 (14) 



1 



2 













11 



8 



1 



2 





2 







11 



9 



1 



2 





2 







11 



9 



1 



Limnetis . 

 Estlieria . . 

 Iiimnadia . 

 Apus 



Artemia , 



Branchinecta 

 Branchipus .., 



17-19 

 29-33 



28 

 47 



25 

 2(5 

 26 



* Second antennae sometimes wanting. tThe endite wanting in the American species ot Aptis. 



In an Apus lucasanus 42 millimeters in length there are 60 pairs of 

 legs behind the maxillipedes. There are 42 segments behind the max- 

 illipedal segment, including the telson, and 27 limb-bearing segments, 

 or GO pairs of legs to 27 segments, the average being 2-2^^- appendages to 

 each leg-beariug segment. On the first eleven leg bearing arthromeres, 

 or the 10 thoracic (bsenomeres) together with the first abdominal arthro- 

 mere there is but a single pair of appendages to a segment, so that there 

 are 49 pairs of abdominal appendages to IG arthromeres, or o^V pairs of 

 limbs on the average to each abdominal arthromere. The fourteenth, 

 fifteenth, and sixteenth pairs are situated on two arthromeres, and so 

 on with the succeeding until the limbs become more numerous. On the 

 two arthromeres before the last leg-bearing one there are 12 pairs of 

 appendages, or G to each arthromere. 



This irrelative repetition of arthromeres is only paralleled in one other 

 Branchiate group, the TriloUta. In this group the new segments are 

 interpolated between the head and abdomen at successive moults, as 

 shown by Barrande. 



The grouping of the body segments into a cephalothorax and abdo- 

 men, comparable with those two regions in the Decapoda is but slightly, 

 if at all, indicated in the Phyllopoda. In Limnetis there is no such dis- 

 tinction of regions, in Apus the cephalothorax merges insensibly into the 



