MANUAL OF NATURAL HISTORY. 297 



II. SUB-ORDER NATATOKY-ISOPODS (Natatoria). 



Mouth with two pairs of jaws besides mandibles 

 and foot-jaws ; hind false-feet ending in horizontal 

 laminae, which form with the last segment of the 

 .abdomen, a caudal fin. 



5. FAMILY. Pranisians (Pranizidse). Head united 



to the first two thoracic rings ; antennae seta- 

 ceous ; thorax composed of five rings ; the 

 two first pairs of legs rudimentary or want- 

 ing, five last pairs of legs slender, ambula- 

 tory ; abdomen narrow, but greatly deve- 

 loped. 



6. FAMILY. Sphceromids (Sphseromatidse). Body 



oval, convex; thorax of seven moveable rings ; 

 seven pairs of legs nearly equal; abdomen 

 short ; foot-jaws palpiform ; first five rings of 

 abdomen soldered together, hind false-feet 

 ending in two lamellar appendages, the outer 

 one only moveable ; head large ; legs simply 

 ambulatory. 



7. FAMILY. Fish-Lice (Cymothoidse). Body oval ; 



head small ; thorax of seven moveable rings; 

 seven pairs of legs, nearly equal ; abdomen 

 very short ; foot-jaws opercular ; first five 

 segments of abdomen not soldered together, 

 last false-feet ending in two moveable la- 

 minae ; legs short and hooked. Parasitic on 

 fish. 



III. S UB-ORDER. SEDENTAKY-ISOPODS (Sedentaria). 



Mouth without jaws, but with distinct mandibles 



o 5 



