A REVISION OF THE BRITISH IDOTEID^. 747 



it is recorded by Norman and Tattersall), also from the Adriatic and Mediterranean 

 Seas, Japan, and the Atlantic coast of North America. Recorded also from Greenland, 

 Iceland, and Patagonia (Richardson) ; New South Wales and Borneo (Miers). 



Remarks. — This species is widely separated from any other British species. It 

 approaches /. emarginata (Fabr.) in the form of the cephalon and uropoda, and less 

 so in the form of the coxal plates of the mesosome. In the form of the antennules 

 and antennae, the first maxillae, the maxillipedes, and in the shape of the metasome, 

 there are marked differences. The maxillipedes are short and broad, whilst in 

 I. emarginata they are narrow and elongated. Miss Richardson (58, p. 363, fig. 

 393) wrongly figures the coxopodite as a single piece, and Stephensen's figure 

 (73, p. 13, fig. 4) of I. metallica is really of a new and allied species which I am 

 describing elsewhere. The lateral margins of the metasome in 1. metallica are 

 straight, whereas in I. emarginata they are slightly curved. 



On the posterior region of the cephalon there is in this species a deeply impressed 

 transverse furrow. Referring to this, Tattersall (75) remarks that this species 

 " may be distinguished from I. emarginata very readily by the presence of a small 

 supplementary segment between the cephalon and the first segment of the thorax.'.' 

 The term " supplementary segment" is somewhat unfortunate, as examination shows 

 that this furrow is in no sense a segment or even a suture indicating one, but simply 

 the sinuous line, common to a large series of genera and species of this family, near 

 the posterior margin of the cephalon. In I. baltica and other species it is laterally 

 continued as a cleft ; in J. metallica this is not so, only it is more deeply impressed. In 

 the closely allied species (the I. metallica of Stephensen) this is not so pronounced. 

 Somewhat similar lines or furrows are present on the segments of the mesosome in 

 many species of Isopoda, and as a sinuous line it is present on the cephalon of 

 I. baltica, I. neglecta, I. pelagica, I. emarginata, 1. linearis, and many other species. 



There is perhaps less difference in the form of the body in the two sexes in this 

 species than in any other British species of the genus. 



(9) Idotea linearis (Pennant). (PI. IX, figs. 92-102.) 



Onisrus linearis, Pennant, Brit. Zool., 1777, vol. iv, pi. xviii, fig. 2. 



Idotea fridenlata, Latreille, Gen. Crust, et Ins., 1806, vol. i, p. 611. 



Idotea hectica, Leach, Edinb. Encycl., 1833, vol. vii, p. 404 (nee Pallas). 



Stenosoma lineare, Leach, Trans. Linn. Soc. Lond., 18 J 5, vol. xi, p. 366. 



Idotea linearis, Milne-Edwards, Hist. Nat. Crust., 1840, vol. iii, p. 132. 



Idothea sexlineata, Kroyer, Naturhist. Tidssk., 1846 (s. 2), vol. ii, p. 88; Voyage en Scand., etc., pi. xxvi, 



fig. 1. 

 Idotea linearis, Bate and Westwood, Brit. Sessile-eyed Crust., 1868, vol. ii, figures on p. 388; Miers, 



Joum. Linn. Soc. Lond., 1881, vol. xvi, p. 47; Norman, Ann. and Mag. Nat. Hist., 1904 (s. 7), 



vol. xiv, ]>. 443 ; Tattersall, Nord. Plank., 1911, p. 229, fig. 117. 



Body narrow, elongated, somewhat depressed dorsally, surface uneven. Cephalon 

 (fig. 92) wider than long, with anterior margin deeply emarginate, lateral lobe 



