BRANCHIOPODA. CLADOCERA. 377 



dorsal, not stalked ; caudal fork consisting of two long jointed appendages ; 

 both pairs of antennae simple and rudimentary ; two pairs of maxillae 

 are present. There are 40-63 pairs of legs diminishing from before 

 backwards, and furnished with two exites ; the terminal appendages 

 of the most anterior pair are long and antenna -like ; and the llth are 

 modified to form round brood-pouches in the female (cf. p. 376). 



Single fam. Apodidae. Apus Schaff. without median caudal lamella. 

 Lepidurus Leach, with a median caudal lamella, and larger carapace, but 

 the 2 genera closely allied. Many spp. known from fresh waters in many 

 parts of the world. 



Tribe 3. CONCHOSTRACA. 



A bivalve shell is present in which the whole of the rest of the body 

 may be completely enclosed. Lateral eyes not stalked, approximated. 

 First antennae simple, small or rudimentary ; second large and biramous. 

 1028 pairs of post-cephalic limbs are present, of which the first, or the 

 first and second pairs, are provided with prehensile hooks in the male. 

 The eggs are carried between the hinder part of the body and the shell, 

 attached to dorsally directed processes of some of the limbs. 



Fam. 1. Limnadiidae. Shell compressed, marked with lines of 

 growth ; body elongated, with 16-28 pairs of thoracic legs. Limnadia 

 -Brong. ; Eulimnadia Packard ; Estheria Riipp. ; Leptestheria G.O.S. 

 Cyclestheria G.O.S. 



Fam. 2. Limnetidae. Shell tumid, without lines of growth ; head 

 very large ; body short ; not more than 12 pairs of legs. Limnetis Loven. 



Sub-Order 2. CLADOCERA. Water-fleas.* 



Small laterally compressed Branchiopoda, whose body, with the 

 exception of the head, which projects freely, is usually enclosed in 

 a bivalve shell. The second antennae are large and are used in 

 swimming, and there are four to six pairs of swimming feet. The 

 epipodites may be absent. 



The Cladocera are small simply organized Branchiopoda, 

 whose resemblance to the larvae of the shelled Phyllopods, par- 

 ticularly to that of Estheria with its six pairs of legs, probably 

 gives the best indication of the origin of the group. Unlike 



* Besides the work of F. Leydig already quoted compare H. E. Strauss- 

 Diirkheim, " Memoire sur les Daphnia de la classe des Crustaces," Mem. 

 du Mus. d'hist. nat., Tom. V and VI, 1819 and 1820. Leydig, Natur- 

 geschichte der Daphniden, Tubingen, 1860. P. E. Miiller, Bidrag til 

 Cladocerernes Fortplantings historic, Kjobenhavn, 1868. G. O. Sars,," Om en- 

 dimorph Udvikling samt Generationsvexel hos Leptodora," Vidensk. 

 Selsk.Forh.,Christiani&, 1873, p. 1. A Weismann, Beitrage zur Kenntniss 

 der Daphnoiden, I VII, Z. f. w. Z., Tom. 27, 28, 30 supl, and 33, 1876-1880. 

 C. Glaus, Zur Kenntniss der Organisation, etc., der Daphniden, ibid., 27, 

 1876. C. Glaus, Zur Kenntniss des Baues und der Organisation der Poly- 

 phemiden, Wien, 1877. C. Grobben, Die Embryonalentwickelung von 

 Moina rectirostris, Arbeiten aus dem zool. Institut. Wien, II Band, 1879. 

 W. A. Cunnington, Studien an einer Daphnide, Jena. Zeits., T. 37, p. 447, 

 1903. 



