PHYLLOPODA. 



347 



Most of the living Phyllopods are inhabitants of fresh 

 waters, but some live in the sea (Nebalia), and others affect 

 waters which are abnormally salt (Ariemia). The two most 

 interesting recent forms, as bearing on fossil examples of the 

 order, are Limnadia and Apus, both of which live in fresh 

 water. In Limnadia the body is enclosed in an oval bivalve 

 carapace, and there are from eighteen to thirty pairs of 

 membranous leaf-like feet. In Apus the carapace is clypei- 

 form, and protects a considerable portion of the abdomen ; 

 and there are sixty pairs of feet, of which all but the first 

 pair are foliaceous. 



Fig. 202. Morphology of recent Phyllopoda. A, Lepidurus Angassi, viewed dorsally ; B, 

 Under side of head of the same ; c, Nebalia bipes, one side of the carapace being removed, so 

 as to show the branchial feet ; D, Branchipus stagnalis, female ; E and F, Young stages of the 

 same ; G, A magnified specimen of Estheria, in its living state. 



Leaving out of sight the genera Estheria and Leaia, the 

 Phyllopods are almost exclusively Palaeozoic in their distribu- 

 tion, and are chiefly, though not exclusively, known by their 

 carapace-valves. The best-known genera are the Hymeno- 

 caris of the Lingula flags ; the Caryocaris of the Skiddaw 

 Slates ; the Peltocaris and Discinocaris of the Silurian, with 

 their allies Aptychopsis, Pterocaris, and Cryptocaris; the Ceratio- 

 caris of the Silurian, Devonian, and Carboniferous ; and the 

 Dithyrocaris of the Carboniferous Limestone. These forms 

 have a general resemblance to one another, and are believed 

 to be most nearly allied to the recent Apus, whilst they are 



