79 



being sometimes pronouncedly subcheliform in structure. The anterior pairs of 

 pleopoda with the rami densely setiferous, 2nd pair in male with the usual stylet. 

 Uropoda very large, lamellar, valve-like, closing over the lower face of the meta- 

 some; outer part cut off by a transverse suture, and forming a separate plate, in- 

 side which sometimes occurs another much smaller plate. Incubatory pouch normal. 

 Remarks. — This family is chiefly distinguished from the Arcturidce by the 

 more or less broad, depressed body, the rather uniform segmentation of the meso- 

 some, and the structure of the legs. Some of the largest known Isopoda are in- 

 cluded in this family. Thus the huge Gtyptonotus amtarcticus measures no less 

 than 3 inches and a half in length, and some of the arctic species of the genus 

 Chiridothea are scarcely smaller. The family comprises about 10 genera, only 

 one of which is represented in the fauna of Norway. 



Gen. IdOthea, Fabr., 1798. 



Generic Characters. — Body oval or oblong, distinctly depressed, with the 

 coxal plates, beyond the 1 st segment of mesosome, well defined, laminar. Cephalon 

 subfljuadrate, with the lateral parts not expanded. Metasome with 3 short seg- 

 ments exposed in front of the terminal one, the 3rd segment being, however, less 

 perfectly defined dorsally. Eyes distinct, lateral. Superior antenna 1 with the 

 flagellum short, clavate; inferior antenna? with the flagellum more or less elongated 

 and multiarticulate. Mandibles very strong, with the cutting edge divided into 2 

 superposed dentated lamelhe, molar expansion large and thick. Both pairs of 

 maxilla? of quite normal structure. Maxillipeds with the palp 4-articulate, last 

 joint lamellarly expanded, masticatory lobe well developed, epignath oblong oval, 

 turned in front. Legs of rather uniform structure, ambulatory, and as a rule 

 more strongly built in male than in female, sometimes approaching to a subcheli- 

 form character, dactylus in all pairs strong, unguiform, unequally bidentate at the 

 tip. Uropoda terminating in a single flattened joint, and having at the base 

 of this joint, outside, a strong ciliated seta. Male, as a rule, much larger 

 than female. 



Remarks. — This is the genus first established, and it accordingly may be 

 regarded as the type of the family. Numerous species have been described by 

 different authors from different parts of the Oceans, bat some of these ought 

 certainly to be separated generically, and even in the restriction adopted by Mr. 



