86 ME. E. J. MIEES OK THE IDOTEIDJ:. 



Idotea ai'gentea, Dana, Amer. Journ. of Sci. Sf Arts, (ser. 2) viii. p. 426 



(1849); id. U.S. Explor. Exped.,Crust. xiv. p. 698, pi. xlvi. fig. 1 (1853); 



Miers, Cat. New-Zealand Crust, p. 92 (1868). 

 Idotea annulata, Dana, Amer. Journ. of Sci. 8r Arts, (ser. 2) viii. 



p. 426 (1849); id. U.S. Explor. Exped. xiv. Crust, p. 701, pi. xlvi. 



fig. 3 (1853); Cunningham, Trans. Linn. Soc. xxvii. p. 499 (1871) ; 



nee Miers, Proc. Zool. Soc. p. 7^ (1881). 



This species is obloug-oval, moderately convex, the somewhat 

 projecting epimera usually giving, in the adult, a serrated 

 appearance to the sides of the thorax. The head is transverse, 

 with the anterior margin slightly concave ; the antero-lateral 

 angles roanded and but little prominent; near the posterior 

 margin of the head is a deeply impressed arcuated transverse 

 furrow. The surface of the body is more or less rugose ; the 

 lateral sutures on the dorsal surface of the postabdomen posterior 

 to the second segment are strongly marked, nearly straight, and 

 directed obliquely upward toward the middle line of the body ; 

 the terminal segment is convex, nearly oblong, rounded at the 

 postero-lateral angles; posterior margin square -truncated, or very 

 slightly excavated, or with a veiy obscure median denticle. 

 The eyes are large and prominent. The termuial joint o£ the 

 peduncle of the antennae- longer than the preceding ; the fla- 

 gellum short, usually 7-10-joiiited. The epimera are well deve- 

 loped, with the postero-lateral angles subacute and usually some- 

 what projecting in the adult ; the basal plate of the opercular 

 valves is oblong, with parallel sides ; the terminal plate nearly 

 square, but rounded off at its externo-distal angle. The length 

 of an adult male may exceed 1 inch (28 millira., Harger) ; but 

 the majority of the specimens in the Museum collection do not 

 exceed f inch (17 millim.). 



The colour, according to Harger, is bright blue or green when 

 alive, becoming darker and duller in alcohol, without the markings 

 of the other species, but often with metallic reflections. In by 

 far the greater number of specimens that I have seen, whether 

 preserved dry or in spirit, the lateral margins of the epimera are 

 paler, and there is a more or less distinct transverse band of pale 

 colour on the jDOsterior margin of the terminal segment. 



The robust antennae, large eyes, rugose thoracic segments, and 

 square- truncated terminal postabdominal segment will always 

 distinguish this species from varieties of Idotea fnarina with the 

 lobes of the terminal segment obsolete. 



This is apparently a very common and almost cosmopolitan 



