(21) 



FAMILY (JAMMARIDAE. 



Both antennae well developed, the upper long, slender, filiform, usually 

 immediately above the lower, which are inserted into a notch at the front 

 angle of the head. First and second feet sub-chelate. Eyes compound, 

 commonly between upper and lower antennae. 



Genus Gammarus. 



No rostrum. Three last abdominal segments each with two or more 

 clusters of short stitF spines on hind margin. Secondary flagellum and man- 

 dibular palpus present. Last pair of abdominal legs two branched; telson 

 double. 



G. fmciatu!^, Saij. Secondary flagellum as long as second segment 

 of peduncle (19'i, and composed of five or six segments. Fourth, fifth and 

 sixth abdomi'i'il segments each with three clusters of spines on hind margin. 



Genus Crangonyx. 



No clusters of spines on posterior abdominal segments. Telson single ; 

 last pair of abdominal legs with inner branch rudimentary or wanting. Pe- 

 duncles of the two pairs of antennae sub-equal. The first two pairs of 

 feet sub-equal. 



C. (jracUiy, Smith. Eyes evident. Hind angles of first three abdom- 

 inal segments each ending in a sharp tooth. Outer branch of last pair of 

 legs about twice as long as peduncle ; inner branch very small. Telson 

 short, euiarginate. 



C. mucronatuf, Forbes. No eyes. Hind angles of first three abdomi- 

 nal segments rounded. Outer branch of last pair of legs shorter than pe- 

 duncle, inner minute. Telson of male a slender spine about as long as 

 first three abdominal segments. 



ORDER ISOPODA. 



Body commonly depressed ; thoracic segments not consolidated ; eyes, 

 if present, compound, sessile. Gill plates beneath abdomen. The last 

 four pairs of thoracic legs similar, and difl"ering from the first three pairs. 

 Last pair of abdominal legs more or less styliform. 



FAMILY ONISCIDAE. 



Abdomen many-jointed, last segment small, caudal stylets (20)well ex- 

 serted. Mandibles without palpi. Inner antennae obsolete. 



FAMILY ASELLIDAE. 



Body very flat, loosely jointed. Last abdominal segment very large, 

 shield-like, comprising nearly the whole abdomen. LTpper antennae short, 

 lower very long. Only first pair of feet sub-chelate. Mandibles with 

 palpi. 



Genus Ascllus. 



First pair of feet sub-chelate ; last thoracic legs not elongate ; first 

 pair of abdominal appendages in female (first two pairs in male) small, 

 forming short plates; outer ramus of next pair serving as gill-covers; cau- 

 dal stylets elongate. 



