ISOPODS OF NORTH AMERICA. 215 



ANALYTICAL KEY To TIIR (iKNKKA OF THE FAMILY CYMOTIIOID.E. 



, Head posteriorly imxluced in three lobes, a larger median lobe and two small 

 lateral lobes; not at all iiuniersed in first thoracic sejjment. Anterior inar>xin of 

 first thoracic segment distinctly trisiimate. 

 /;. Uropoda and terminal scirnient ciliated. Eyes large, conspicuous. 



(Jenus .T'^galhoa Dana 

 //. I'ropoda and terminal segment not ciliated. Eyes small. 



c. Posterior angles of first segment of body prominent or produced, YCry often 

 acute; posterior angles of the following segments increasing gradually in 

 length, the first of these very often scarcely produced, the posterior ones 

 very often produced, abruptly longer than the first. Epimera of the first 

 segments extending beyond the posterior angles of the segment; posterior 



ones produced, acute (Tcnns Ncrocila Leach 



c^. Posterior angles of first six segments of l)ody scarcely or not at all j)romi- 



nent, those of seventh segment produced. Epimera of first segments very 



often almost reaching, or not reaching by a short distanct', the posterior 



angle of the segment. 



d. Body compact. Head not constricted at the base. I'ropoda very often 



more or less longer than terminal segment. Legs gradually increasing in 



length (lenus Anilocra Leach 



d'. Body relaxed. Head constricted at the base. Uropoda much shorter than 

 terminal segment. Legs gradually much longer successively; seventh 



pair abruptly very nmch longer Genus Olencira Leach 



'. Head not produced posteriorly in three lobes; more or less immersed in first 



thoracic segment. Anterior margin of first thoracic segment not trisinuate. 

 /;. Antennte very much dilated; those of the first pair contiguous at base. 



c. Epimera of the first pair with a carina produced in the foi-m of a sj)oon in 

 female. Ungulfe very long, unequal in length; those of the third pair 

 longest, abruptly longer than second pair. Terminal segment trans- 

 verse (ienus Ccratotlioa Dana 



c^. Epimera of the first pair not produced in female. LTngulje mostly very short, . 

 very rarely long, ecjual in length. Terminal segment subtriangular, semi- 

 circular, often bilobed Genus Mchtertia Stebbing 



//. Antennae not dilated, but compressed. 

 c. Antennte of the first pair almost contigu<^)Us at ])ase. 



d. Body hunched or compressed; the posterior segments of the body on one 



side flattened, dilated Genus Agarna Bchitiedte and Meinert 



d'. Body evenly convex, not hunched; posterior segments of the body rather 



convex Genus Indusa Schio'dte and Meinert 



c^. First pair of antennae widely separated at the base. 



d. Abdomen manifestly separated from the thorax, al)ruptly narrower than 



thorax (iemis Ci/niollida Fa))ricius 



d^. Abdomen continuous with thorax, not narrower than thorax. 

 e. Abdomen very little or scarcely iimnersed. Segments of thorax either 

 equal in length or the first segment aljruptly longer and the last segment 



abruptly shorter than the others ...Genus Livoneca Leach 



V. Abdomen very deeply and profoundly immersed. First segment of the 

 thorax manifestly longer than the second; six posterior segments gradu- 

 allv decreasing a little in length ...Genus Irona SchiaHlte and >h^incrt 



