MARINE ISOPODA OP ISTEW ENGLAND, ETC. 34^ 



Zdotea robusta Kroyer. 



f Idotea vietaUka Bosc, Hist. nat. des Crust., torn, ii, p. 179, pi. 15, fig. 6, 1802. 

 Idothea rohmta Kroyer, Naturhist. Tidssk,, II, B. ii, p. 108, 1846; Voy. en Scand.^ 

 Crust., pi. 26, fig. 3, "1849." 

 Reinliardt, Groulands Krebsdyr, p. 35, 1857. 

 Stimpson, Proc. Acad. Nat. Sci., 1862, p. 133, 1862. 

 Verrill, Am. Jour. Sci., Ill, vol. ii, p. 360, 1871; This Report, part i, p. 



439 (145), 1874 (Idotea). 

 Harger, This Report, part i, p. 569 (275), pi. v, fig. 24, 1874; Proc. U. S. 



Nat. Mus., 1879, vol. ii, p. 160, 1879 (Idotea). 

 Liitken, Crustacea of Greenland, p. 150, note, 1875. 



Plate VI, Figs. 30-32. 



This species is easily recognized withiii the genus by the pleon, which 

 is broadly truncate at the apex and not at all pointed. The pleon is alsa 

 large and more swollen above than in the other species. For characters 

 separating it from other Isopoda, see near the close of the generic des- 

 cription. 



The entire upper surface, except perhaps that of the pleon, is some- 

 what rugose. The head is nearly square, with the eyes large and prom- 

 inent. The antennae (pi. VI, fig. 31 a) have the second segment large, the 

 flagellum short, usually of less than ten articulations. Under a sufficient 

 power these organs are seen to be clothed with a very fine close pubes- 

 cence, which also occurs in a less degree upon the legs. The maxillipeds 

 (pi. VI, fig. 32 a) have the external lameUa (1) short and oval. 



The legs are robust and spiny. The epimera, projecting, give a ser- 

 rated appearance to the sides of the thorax, as seen in figure 30, plate 

 VI, and the dorsum is more convex than in the other species. 



The pleon is large and convex, its sides are nearly parallel beyond the 

 middle, and it is broadly truncate, or even somewhat emarginate, at the 

 apex. The basal plate of the operculum (pi. VI, fig. 31c) is elongated, 

 with parallel sides; the terminal plate less than one-fourth as long and 

 nearly square, but tapering slightly and somewhat broader than long. 

 The male stylet on the second pair of pleopods (pi. VI, fig. 32 c, s) reaches 

 the end of the lamella, to which it is attached, and is slightly curved and 

 rounded at the tip. 



Length of male 28°'™; female 22'°°»; breadth 9°^'». Color bright blue 

 or green above when alive, becoming darker and dull in alcohol, with- 

 out the markings of the other species, but often with metallic reflections, 

 when seen in the water, where it is commonly taken swimming free or 

 among masses of floating sea- weed. 



It is thus found in mid-ocean, and was described by Kroyer from speci- 

 mens taken in about 60° north latitude between Iceland and Greenland. 

 It was taken in considerable abundance at Fire Island Beach !, on the 

 south shore of Long Island, by Professor S. I. Smith in 1870; also by the 

 U. S. Fish Commission at Vineyard Sound !, Mass., often in company with 

 I. irrorata Edw.; at George's Banks!, September, 1872, small specimens, 

 5mm ill length; between Boon Island and Matinicus Eocks, near the 



