732 



ARTHEOPODA 



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 f urea, 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 differs from that 

 commonly adopted, in that the term Phyllopoda (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. Instead, 

 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 Glaus and some writers following him is 

 contrary to the rule.^ 



Order 1. ANOSTRACA Sars. 



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

 nineteen pairs of trunk -limbs, none post - genital ; f ureal rami 

 unsegmented, rod-like or flattened. 



Branchipodites Woodward. Similar to the Recent Branchi- 

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

 Woodw. 



Opabinia, 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 - 

 limbs forty to sixty-three pairs, of ivhich 

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

 furcal rami multiarticulate. 



Fig. 1413. 



Yohoia tenuis WaUtott. 

 Middle Cambrian ; Britisli 

 Columbia. Dorsal view, 



X2/i. 



Protocar is Walcott (Fig. 1414). This 

 is the oldest representative of the Apus- 

 type, and exhibits a remarkable similarity 

 to A2)us in its univalve carapace, multi- 

 segmented abdomen, and single pair of 



Lower Cambrian ; Vermont. 



Pig. 1414. 



Prolocaris marshi Walcott. 

 Lower Cambrian ; Georgia, 

 Vermont, x %. 



caudal spines 



1 Unfortunately some writers, following Glaus, have transposed the names Branchiopoda and 

 Phyllopoda, applying the latter to the superorder and the former to one of its divisions, but this 

 use is not sanctioned either by priority or by universal custom. 



