730 



ARTHROPODA 



PHYLUM VII 



Subclass B. EUCRUSTACEA Kingsley/ (Crustacea proper.) 



Crustacea having typically two pairs of antenniform preoral appendages and at 

 hast three pairs of postoral appendages acting as jaws. 



In the Crustacea proper the appendages of the head-region are as follows : 

 the first and second pairs are preoral and are known respectively as antennules 

 and antennae ; the third pair, placed on either side of the mouth, are the 

 mandibles; the fourth pair, maxillulae, and fifth pair, maxillae (the two pairs 

 sometimes known as first and second maxillae), are secondary jaws. The 

 appendages behind these vary in character, some being Walking or swimming 

 feet, while from one to three pairs may be subsidiary to the maxillae in 

 feeding, in which case they are called maxillipeds. 



Regarding the evolution of the subclass, Bernard has reached the conclusion 



I 



1 



Strabops ■ 



Sidneyia • • 



Agiaspis 

 Mobria 



Emeraldella'- . 

 Habelia 



y 



NathorsUa 



•Mauella 



Bidentia 



-Hymenocaris 



, Opabin 



Beltina^ 



Theoeetical Evolution of Cambrian Crustacea from the Branchiopoda 

 (accordmg to Walcott 2). 



ilT'firü^Z""*'"^ are descended from a browdng carnivorous annelid with 



md! n L "ir;"^ ? PÜ-T'"* ^°' P"^*^'"« f°°d into its mouth. The 

 Be.trd TZf'^'r .i'^'^'^^'P'''''^*'"^' crustacean-annelid, according to 

 fauna otß itÄ,„ W ^' ^"«ess shale (Middle Oambriän) crustalan 



whTh have the L Hh \T' "'"*'" *"'"^"<^^' ^^' ^''»«^ W«^« Walcott, 

 Wh ch have the head bent down so that the mouth faces posteriorly, and in 



Literature: Öerstoec^-er, yi. and Ortoj««« a v n ^ ■ ^ , 



des Thierreichs, vol. v., 1866-1901 — rl/T w/ m' ^^^«^^^ea, in Bronn's Klassen und Ordnungen 

 pt. vii., fasc. 3, 1909. ' ^""'^^» '^- ^^ Crustacea, in Lankester's Treatise on Zoology, 



Smithson! mL^oU.', 1912!'voLTvi[!^no.^r'^'''^°'^^' ^^^^«««t^^««' Trilobita, and Merostomata. 



J 



