A REVISION OF THE BRITISH IDOTEID^E. 743 



(fig. 49) with first joint expanded, second less so, third elongated and somewhat 

 expanded distally ; flagellum clavate. Antennae (figs. 50 and 51) stout, first three 

 joints almost subequal, fourth longer, fifth longest ; flagellum with sixteen joints. 

 First maxillae (fig. 52), outer lobe terminating in eleven curved spines, inner lobe 

 with three setose spines. The segments of the mesosome (fig. 56) are almost sub- 

 equal, except the first, the coxal plates occupy the anterior two-thirds of the 

 lateral margin of the second segment, the third rather more, and the remainder 

 the whole of the lateral margins, increasing in breadth from the fourth to the 

 seventh segments. Maxillipedes (fig. 53) with four-jointed palp, groove on the 

 third joint small, basal plate elongated, with narrow epipodite extending to the 

 third joint of the palp ; inner lobe also narrow. Thoracic appendages (figs. 54 

 and 55), first short and stout, gradually becoming larger from the second to the 

 seventh. Metasome (fig. 57) composed of two narrow segments and lateral sutures 

 indicating a coalesced third, the terminal segment tapering to a pointed extremity 

 with the lateral angles rounded. Uropoda (fig. 58) flattened, elongated, rounded 

 anteriorly, sides nearly parallel, inner margin posteriorly extended, exopodite bluntly 

 pointed posteriorly, anterior margin convex, short setose style. 



Length of c? 19 to 21 mm., of £ 16 mm. 



Colour (in alcohol) light reddish, or yellowish-brown with minute black dots. 



Geographical Distribution. — St Andrews Bay, Firth of Forth, Isle of Wight ; Bay 

 of Nigg (Scott) ; Port Erin Bay (Hewitt) ; Northumberland, and Berehaven, Ireland 

 (Norman) ; South and West Ireland (Tattersall) : also Norwegian coast (G. 0. Sars). 



Remarks. — The narrow lanceolate form of the terminal segment at once serves 

 to distinguish this species from any other member of the genus. Sars (64) states 

 that the coxal plates are " comparatively small," but in all the British specimens 



1 have examined they are as figured (PI. V, fig. 56). Examples received from 

 Professor Sars are rather smaller than ours, the largest being 18 mm. in length, 

 but the coxal plates are, comparatively, only very slightly smaller on segments 



2 and 3. That there is considerable variation in size in different localities is 

 evident. Sars gives the length of the male and female as 15 and 11 mm. respec- 

 tively, whereas those I have examined from this country average 19 and 16 mm. 

 Harger (32) states that the length of his 1. marina, var. phosphorea. was 25 mm. 



Although the dorsal surface is usually finely granulated, specimens with a 

 perfectly smooth surface are by no" means rare. 



(6) Idotea sarsi, n. sp. (PL VI, figs. 59-69.) 

 Body oblong oval, moderately convex, dorsal surface rough. Cephalon (fig. 59) 

 wider than long, anterior margin emarginate, posterior margin narrower than the 

 anterior one. Eyes fairly large, situated dorso-laterally. Antennulse (fig. 60) with 

 first joint expanded, second joint small, third joint elongated ; flagellum single clavate 

 joint, slender. Antennae (figs. 61 and 62) short, first joint small, fifth joint with 



