5io 



CRUSTACEA. 



present, the larger pair being of large size, branched, a?id acting as 

 natatory organs. 



The types of this order are mostly confined to fresh water, a few 

 forms being found in brackish pools. No undoubted representa- 

 tives of the Cladocera have been hitherto detected in the fossil 

 state, though a few small fossil types have been referred to this 

 order. 



Order II. Phyllopoda. — Crustacea, mostly of small size, gener- 

 ally having the front part of the body protected by a shield-like cara- 

 pace, or sometimes having the body enclosed i?i a bivalve shell. The 



feet a?x usually numer- 

 ous, and more or fewer 

 of the 711 are leaf like in 

 form, and act as respira- 

 tory organs. 



The living types of the 

 Phyllopods {Apus, fig. 

 362, Bra nchipus, Lim- 

 nadia, Estheria, &c.) 

 are mostly inhabitants of 

 fresh water, but species 

 of Estheria are found in 

 brackish water, and the 

 Artemice. live in salt 

 lakes, or in the brine- 

 pans of salt-works. As 

 a type of the Phyllopods 

 the recent genus Apus 

 (fig. 362) may be taken, 

 in which the anterior 

 part of the body is 

 covered with an oval 

 carapace, carrying a pair 

 of compound eyes upon 

 its upper surface in front. 

 The under surface carries 

 sixty pairs of feet, of which the first is divided into three slender 

 whip-like branches on each side, while the others are of the genuine 

 " phyllopodous " type, being leaf-like in form, and acting as breath- 

 ing-organs in function. 



If the recent genus Nebalia and its numerous fossil allies are 

 removed to form the order Phyllocarida, then the number of known 

 fossil Phyllopods is comparatively small. By far the most important 

 type, from a palaeontological point of view, is the genus Estheria 

 (fig. 363, a), which is nearly related to the living Limnadia, and 



Fig. 362. — Apus cancriformis, a recent Phyllopod, 

 viewed from above, and enlarged. 



