738 DH WALTER E. COLLINUE. 



Idotea marina, Miers, J own. Linn. Soc. Land. {Zool.), 1881, vol. xvi, p. 25. 



Idothea ha/lira. G. O. Sars, Crust. Norn:, 1897, vol. ii, p. 80, pi. xxxii ; Richardson, Bidl. 54, U.S. Nat. 



Mu^., 1900, p. 364 ; Tattersall, Nord. Plan!,:, 1911, p. 219, figs. 83-87. 

 Idotea balthica, Norman, Ann. and Mag. Nat. Hist., 1904 (s. 7), vol. xiv, p. 441. 



Body oblong oval, moderately convex, dorsal surface perfectly smooth. Ceplialon 

 (fig. I ) wider than long, slightly emarginate anteriorly, posterior margin almost 

 straight, posteriorly with lateral clefts continuing inwardly as dorsal ridges. Eyes 

 large, round, situated dorso-laterally, slightly anterior to the median transverse line. 

 Antennulse (fig. 2) extending to the end of the third peduncular joint of the antennae, 

 first joint expanded, irregularly angular, second joint broad but rather smaller, third 

 joint elongated ; flagellum single-jointed, clavate, with nine or ten groups of spatulate 

 setae,. Antennae (figs. 3 and 4) elongated, first peduncular joint very short, second 

 longer and deeply incised ventrally, third and fourth increasing in length, but 

 decreasing in diameter ; flagellum normally with twenty Joints, of which the first 

 ten or eleven are somewhat cuboid, remainder elongated and slightly clavate, with 

 terminal style and long setae (fig. 3). First maxillae (fig. 5), outer lobe terminates in 

 ten short curved spines and a single fine- pointed one, inner lobe narrow, terminating 

 in three setose spines. Second maxillae consisting of three laminar setose lobes. 

 The segments of the mesosome, excepting the first, which is shorter, are about equal 

 in length. Coxal plates large, occupying the whole of the lateral margins of second 

 to seventh segments, gradually increasing in width (fig. 12). Maxillipedes (fig. 6) 

 with four-jointed palp, the third joint grooved for the reception of the postero-lateral 

 border of the first (fig. 7), basal segment large, with inner lobe distally, epipodite 

 oblong oval, extending as far as the third joint of the palp. Thoracic appendages 

 (figs. 8-1 1) more or less alike in structure, with few stout setae, first appendage short 

 and stout, remainder gradually becoming larger from the second to the seventh. 

 Metasome (fig. 13) has two short segments and indications of a coalesced third, 

 terminal segment long, slightly convex, with the posterior margin tridentate, median 

 tooth produced as an acute point, extending beyond the lateral ones. Uropoda 

 (fig. 14) flattened, elongated, rounded anteriorly, sides nearly parallel, inner margins 

 sloping obliquely towards the median line ; articulating with the basal plate on its 

 dorsal side is a short setose style ; endopodite flat, posterior margin narrowed and 

 slightly emarginate. 



Length of $ 35 mm., of P 20 mm. 



Colour exceedingly variable. 



Geographical Distribution. — Common all round our coasts. Amongst many 

 others I have the following records : — Shetland, Moray Firth, St Andrews, Firth of 

 Forth, Yorkshire, Norfolk, Suffolk, and Essex coasts, Isle of Wight and South coast, 

 Devon coast (west and south), Llandudno, Blacksod Bay (Co. Mayo), Irish Sea, 

 St Kilda, Firth of Clyde, and Sutherland coast. It is also recorded as occurring on 

 the Scandinavian and European coasts from Holland to the Mediterranean and Black 



