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ARTHKOPODA 



PHYLUM VII 



laterally compressed, shortened, and often indistinctly segmented. The head 

 is sharply demarcated from the rest of the body, and is usually provided with 

 two large eyes sometimes coalesced, in addition to which there is often a 

 a small unpaired eye. The Upper lip is very large, the mandibles have no 

 palps, and the maxillae are reduced or absent. 



The body-limbs are usually foliaceous and lobed on the outer and inner 

 margins. They vary in number from four to more than sixty pairs, and 

 usually all carry gill-plates. The posterior part of the body is without 

 limbs and usually ends in a caudal furca, the rami of which may be filiform, 

 flattened or claw-like. All Branchiopods have the sexes ^distinct. The 

 males are often much less numerous than the females, and the latter 

 reproduce largely by parthenogenesis. 



The Classification of the Branchiopoda here given diff'ers from that 

 commonly adopted, in that the term Fhyllopoda (Latreille, 1802) is not 

 employed for an ordinal division including several groups which are dis- 

 tinguished from the Cladocera chiefly by the greater number of somites and 

 appendages and by the prevalence of metamorphosis in development. Tnstead, 

 these groups of the old division Phyllopoda are more properly assigned the 

 rank of independent Orders, all three being sharply contrasted from one 

 another as well as from a fourth order, Cladocera. Phyllopods in the old 

 sense, therefore, are equivalent to the Orders Anostraca, Notostraca and 

 Conchostraca, as here recognised. The Substitution of the term Phyllopoda 

 for Branchiopoda, in the usage of Claus and some writers following him is 

 contrary to the rule.^ 



Order 1. ANOSTRACA Sars. 



Head distinct, carapace ahsent, paired eyes pedunculate ; thorax with eleven to 

 nineteen pairs of trunJc-Umhs, none post - genital ; furcal rami_ 

 unsegmented, rod-lihe or flattened. 



Branchipodites Woodward. Similar to the Recent BrancU- 

 pus. Oligocene of Bembridge, Isle of Wight. B. vectensis 

 Woodw. 



Opahinia^ Leanchoilia, Yohoia (Fig. 1413), Bidentia Walcott. 

 Middle Cambrian ; British Columbia. 



Order 2. NOTOSTRACA Sars. 



Carapace forming a dorsal shield ex- 

 tending over the anterior segments ; paired 

 eyes sessile ; antennae vestigial ; trunk- 

 limhs forty to sixty-three pairs, of ivhich 

 twenty-nine to fifty-two are post-genital ; 

 furcal rami multiarticulate. 



Protocans Walcott (Fig. 1414). This 

 is the oldest representative of the Apus- 

 type, and exhibits a remaikable similarity 

 to Apus in its univalve carapace, multi- 

 , segmented abdomen, and sinj^le pair of 



caudal spmes. Lower Cambrian ; Vermont. 



Mlopoda, applj.n, 11,,. 1. tte o the superorder and the former to one of its divisions, but this 

 1'} priority or by universal custom. 



Pio. 1413. 

 Yohoia tenuis Walcott 

 Middle Cambriaii ; I5i itisl 

 Columbia. Dorsal viiw 

 X2/i. 



use is not sanctioned citli 



Fig. 1414. 



Frotocaris marshi 

 Lower Cambrian ; 

 Vermont, x 2/3. 



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