296 MANUAL OF NATURAL HISTORY. 



men well-developed; five first pairs of abdominal 

 extremities lamellar, and subserving respiration. 



I. SUB-ORDER. AMBULATORY-!SOPODS (Ambulatoria). 



Mouth with two pairs of jaws besides mandibles 

 and foot-jaws ; hind false-feet styliform or opercular, 

 not forming a caudal fin. 



1. FAMILY. Sea-Centipedes (Idoteidse). Body li- 



near, elongated ; terminal appendages of hind 

 false-feet large, lamellar, opercular, covering 

 all lower surface of abdomen ; not prolonged 

 beyond the last segment, which is scutiform 

 and very large. 



2. FAMILY. Sea-Woodlice (AsellidaB). Body more 



or less elongated ; terminal appendages of 

 hind false-feet styliform and prolonged be- 

 yond abdomen like a tail ; last joint of abdo- 

 men very large, scutiform ; internal antennae 

 small but distinct. 



3. FAMILY. Fork-tailed Sea-Woodlice (Lygiidse). 



Body oval, head small ; terminal appendages 

 of hind false-feet styliform, slender, elongated, 

 completely exposed, and ending in two styli- 

 form appendages ; last joint of abdomen very 

 small, not scutiform ; internal antennae rudi- 

 mentary. 



4. FAMILY. Woodlice-proper (OniscidaB). Body 



oval, convex ; terminal appendages of hind 

 false-feet short, not extending beyond last 

 segment of abdomen, last joint of abdomen 

 very small, not scutiform ; internal antennas 

 rudimentary. 



