ISOPODS OF NORTH AMERICA. 215 



. ANALYTICAL KEY TO THE GENERA OF THE FAMILY CYMOTHOIDjE. 



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

 lateral lobes; not at all immersed in first thoracic segment. Anterior margin of 

 first thoracic segment distinctly trisinuate. 

 b. Uropoda and terminal segment ciliated. Eyes large, conspicuous. 



Genus Jfyathoa Dana 



b'. Uropoda and terminal segment not ciliated. Eyes small. 

 c. Posterior angles of first segment of body prominent or produced, very 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 Genus Nerocila Leach 



c / . Posterior angles of first six segments of body scarcely or not at all promi- 

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

 often almost reaching, or not reaching by a short distance, the posterior 

 angle of the segment. 



d. Body compact. Head not constricted at the base. Uropoda very often 

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



length Genus 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 much longer Genus Olencira Leach 



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



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

 b. Antennae very much dilated; those of the first pair contiguous at base. 

 c. Epimera of the first pair with a carina produced in the form of a spoon in 

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

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

 verse Genus Ceratolhoa Dana 



c / . Epimera of the first pair not produced in female. Ungulae mostly very short, 

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

 circular, often bilobed Genus Meinertia Stebbing 



//. Antennae not dilated, but compressed. 

 c. Antennae of the first pair almost contiguous at base. 



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



side- flattened, dilated Genus Agarna Schicedte and Meinert 



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



convex Genus Indusa Schioedte and Meinert 



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

 d. Abdomen manifestly separated from the thorax, abruptly narrower than 



thorax Genus Cymothoa Fabricius 



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

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

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



abruptly shorter than the others Genus Livoneca Leach 



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

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

 ally decreasing a little in length Genus Irona Schioedte 



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