24 



A SYNOPSIS OF ANIMAL CLASSIFICATION. 



female upon the third from the 



last. 



The numerous Orders included under this sub-class are arranged 

 for convenience into larger groups, which may be designated as " super- 

 orders" or "legions," and which facilitate the classification. 



Super-order i. LEPTOSTRAKA 



(with a single Order) 



Order i . Phyllocarida This group, mostly fossil, con- 

 tains but a single living form, 

 valuable as a link between Ento- 

 mostraka and Malakostraka. A 

 small integumental duplicature 

 covers the head and thorax. The 

 abdomen is 8-jointed, thus depart- 

 ing from the constant number 

 otherwise found in Malakostraka. 

 The feet are like those ofphyllo- 

 pods. 



X Nehalia. 



Super-order 2. AETHROSTRAKA .. Sessile-eyed Malakostraka, with 



free thoracic segments, and with- 

 out carapace. Thoracic append- 

 ages distributed as one pair of 

 maxillipeds and seven pairs of legs. 

 Brood cavity borne between tho- 

 racic legs. 



Order i. Amphipoda Compressed forms, body generally 



bent into a curve. Seven free 

 thoracic somites. Gills upon the 

 thoracic legs. Abdomen with six 

 pairs of legs, of which the first 

 three are used in swimming and the 

 last three form a springing or leap- 

 ing organ. In a few forms the 

 abdomen is reduced. 



X Gammarus, Caprella. 



Order 2. Isopoda Depressed forms with seven free 



thoracic somites. The abdominal 

 appendages are in the form of 



