MANUAL OF NATURAL HISTORY. 295 



I. ORDER — Amphipods (Amphipoda). 

 Palpi of the thoracic extremities vesicular and 

 subserving respiration ; abdomen greatly developed, 

 serving for locomotion ; six pairs of legs, the three 

 first differing in form and use from the three last. 



1. Family. — Sandhoppers (Gammaridae). Head 



small ; fore-legs developed for digging ; foot- 

 jaws very large, covering the entire mouth, 

 ending in four large horny laminae, and two 

 very long jointed palpiform appendages. 



2. Family. — Ryperians (Hyperiidae). Head large ; 



thoracic legs often prehensile ; abdomen end- 

 ing in a swimming fin; foot-jaws moderate, 

 ending in three horny laminae without any 

 palpiform appendages. 



II. ORDER. — Ljemodipods (Lsemodipoda). 

 Palpi of thoracic extremities vescicular, and sub- 

 serving respiration ; abdomen rudimentary, in the 

 form of a small tubercle. 



1. Family. — Skeleton-Shrimps (Caprellidae). Body 



elongated, cylindrical, narrow ; four well-de- 

 veloped antennae ; legs long and slender, fore- 

 legs inserted near mouth, ending in an oval 

 hand. 



2. Family. — Whale-Fleas (Cyamidae). Body de- 



pressed, oval ; head small, second pair of an- 

 tennae very small ; legs short, curved, pre- 

 hensile ; fore-legs inserted under the head, 

 ending in a small sub-cheliform hand, 



III. ORDER.— Isopods (Isopoda). 

 Palpi of thoracic extremities not vesicular ; abdo- 



