500 PROCEEDINGS OF T'lE NATIONAL MUSEUM. tol.xxiii. 



ANALYTICAL KEY TO THE TRIBES OR SUPERFAMILIE.S OF ATLANTIC COAST ISOPODA.^ 



a. Legs of first pair cheliform. Uropoda terminal. Pleopoda, when distinctly 

 developed, exclusively natatory .. I. Chelifera or Tanaioidea (p. 500). 

 a\ Legs of first pair not cheliform. 

 b. Uropoda lateral. 

 c. Uropoda forming togetlier with the terminal segment of the abdomen a caudal 

 fan. Pleopoda for the most part natatory. 



II. Flabellifera or Cymothoidea (p. 505). 

 <"'. Uropoda valve-like, inflexed, arching over the pleopoda, which to a great 



extent are branchial III. Valvifera or Idoteoidea (p. 537). 



//. Uropoda terminal. 

 c. Free forms. 



d. Pleopoda exclusively branchial, generally covered liy a thin opercular plate 



(the modified first pair) IV. Asellota or Aselloidea (p. 550). 



(V. Pleopoda fitted for air-breathing Y. Oniscoidea (p. 560). 



(/. Parasitic forms VI. Epicaridea or Bopyroidea (p. 576). 



I. CHELIFERA or TANAIOIDEA. 



analytical key to the families of chelifera. 



a. Body scarcely attenuated behind. Mandibles without palp. Superior antennae 

 with one multiarticulate flagellum. Anterior maxillee with only a single 

 masticatory lobe and a one-jointed palp; posterior ones quite rudimentary. 

 Second pair of legs ambulatory in character. Epignath of maxillipeds narrow, 

 falciform Family I. Tanaid.e (p. 500). 



a'. Body narrow, produced, depressed. Mandibles with a three-jointed palp. 

 Superior antenna? with two multiarticulate flagella. Anterior maxillte with 

 two masticatory lobes and a two-jointed palp; posterior ones well developed 

 and setose. Second pair of legs with a large, broad, flat hand. Epignath of 

 maxillipeds large, laminar, branchial in character. 



Family II. Apseudid^ (p. 504). 



Famih I. TANAID.E. 



analytical key to the genera of tanaid^. 



a. Pleopoda only three pairs, which are densely setose. Uropoda simple, short, 



single-l)ranched. Eyes present 1. Tanais. 



a'. Pleopoda five pairs. 'Uropoda double-branched. 

 h. Eyes wanting. 



c. Inner branch of uropoda 2-3 jointed. Pleopoda in female very small, or 

 rudimentary. 

 d. Incubatory pouch formed only by two lamelhe issuing from bases of fourth 

 pair of legs. Pleopoda in female rudimentary. Gnathopods alike in both 

 sexes. Mandibles well developed, with cutting edge coarsely dentated. 



2. Cryptocope. 



d'. Incubatory pouch normal. Pleopoda in female small, sometimes wanting. 



Gnathopods in female of normal appearance, band dilated, fingers strong, 



thumb serrulated; in male slender, fingers simple. Mandibles very small 



and feeble in structure, with cutting edge narrow 3. LeptogmdMa. 



(/. Inner branch of uropoda 8-9 jointed. Pleopoda well developed. 



4. Alaotanais. 



^Sars's analytic key has been used with slight modifications. Sars's An Account 

 of the Crustacea of Norway, II. Isopoda (1896), Pts. I, II, p. 3. 



