A REVISION OF THE BRITISH IDOTEIDyE. 737 



elongated multiarticulate flagellum. Maxillipedes operculiform, palps (endopodites) 

 with four joints, basipodite expanded. Metasome composed of three distinct segments 

 and lateral suture lines in front of the long terminal segment. Uropoda laminar, 

 with basal joint and setose spine. Male usually larger than female. 



Key to the British Species of the Genus Idotea. 



I. Body oblong ovate. 



1. Coxal plates wide. 



a. Metasome terminally produced in the middle and extending beyond 



the lateral angles. 



/. baltica (Pallas). 



b. Metasome terminally broad and rounded. 



I. pelagica, Leach. 



/. neglecta, G. 0. Sars. 



c. Metasome terminally marginate. 



I. emarginata (Fabr.). 



•2. Coxal plates rather narrow. 



d. Metasome terminally drawn out and pointed. 



/. granulosa, Rathke. 

 /. sarsi, Collinge. 

 /. viridis (Slabber). 



e. Metasome terminally more or less truncate. 



/. metallica, Bosc. 



II. Body elongated, filiform. 



I. Coxal plates very small. 



a. Metasome terminally emarginate. 



/. linearis (Pennant). 



(l) Idotea baltica (Pallas). (PI. I, figs. 1-1 4.) 



Oniscus hallieus, Pallas, Spic. Zool., 1772, vol. ix, p. 67, pi. iv, fig. 6. 



Idotea entomon, Pennant, Brit. Zool., 1777, vol. iv, p. 38, pi. xviii, fig. 5. 



Stbnotioma irrorata, Say, Journ. Acad. Nat. Sci. Phila., 1818, vol. i, p. 423. 



Idotea tridentata, Rathke, Fauna None, 1843, t. xx, p. 21. 



Idotea tricuspidata, Desmarest, Did. des Sci. Nat., 1823, t. xxviii, p. 373, pi. xlvi ; Roux, Crust, de la 



Medil., 1828, pi. xxix, figs. 11, 12; Milne-Edwards, Hist. Nat. Crust., 1840, vol. iii, p. 129; Sars, 



Fork. Videns/c. SelsJc. Christ., 1859, p. 151 ; Norman, Rep. Brit. Assoc, 1866, p. 197 ; Bate and 



Westwood, Brit. Sessile-eyed Crust., 1868, vol. ii, p. 379. 

 Idotea irrorata, Harger and Verrill, Rep. U.S. Fish Comm., 1873, pt. i, p. 569, pi. v, fig. 23 ; Verrill, 



Am. Journ. Sci. Ads, 1874, vol. vii, pp. 131, 134 ; Harger, Proc. U.S. Nat. Mus., 1879, vol. ii, 



p. 160. 

 Idotea tricuspidata, Stebbing, Journ. Linn. Soc. Lond. {Zool.), 1876, vol. xii, p. 148; Dollfus, Feuille des 



jeunes Nat., 1895, p. 55. 

 TRANS. ROY. SOC. EDIN., VOL. LI, PART III (NO. 23). 108 



