the Isopod Idotea hectica (Pallas). 163 



Idolea hectica (Pallas). 



Body (fig. 1) elongate, narrow-oblong-, slightly narrowed 

 towards the head, convex ; longitudinal median dorsal keel 

 extending from the first mesosomatic segment to the end of 

 the anterior third of the terminal segment, epimera not 

 visible dorsally. Ceplialon convex, anterior margin with a 

 deep, almost semicircular excavation ; lateral lobes broad 

 and obtuse; epistome shallow and produced into a short 

 conical rostrum. Eyes small, situated dorso-laterally. 

 Antennulae (fig. 2) 4-jointed, the first one being stout and 

 broad. Antennae (tig. 3) slightly over half the length of the 

 ceplialon and mesosome, peduncle with the last two joints 

 elongated and subequal ; flagellum multiarticulate. First 

 maxillae (fig. 4) with outer lobe terminating in seven curved 

 spines, the inner lobe with three dense setaceous ones. Second 

 maxillae (fig. 5) short, thin, and plate-like, terminating in 

 three setaceous lobes. The segments of the mesosome are 

 about equal in length, excepting the first, which is somewhat 

 shorter than any of the others, all produced backuardly 

 in the median line to a point which is especially prominent 

 on the sixth and seventh segments ; posterolateral angles 

 not acute. Maxillipedes (fig. 6) thin and flattened, with 

 4-jointed palp, inner basal segment unjointed. Thoracic 

 appendages slender and all similar in character. The abdo- 

 men is composed of three distinct segments, with suture-lines 

 on either side of another partly coalesced segment, the third 

 or terminal segment measuring 14 mm. in length and 4 mm. 

 in width at the base, distally with a semicircular emaigiuatiun, 

 and the postero-lateral angles produced and acute. Uropoda 

 (fig. 7) almost straight on the inner side with prominent 

 raised inner margin, broader posteriorly than anteriorly, 

 terminally the basal plate is oblique; exopodite a small 

 setose spine; endopodite straight on the inner side, slightly 

 curved externally, with posterior margin slightly emarginate. 

 Length 45*5 mm. Colour (in alcohol) fawn with minute 

 decolorized pigment-spots. 



IJab. Atlantic Ocean, 1864 (Mr. Sibbald). 

 According to Miers, Lucas states that the colour is a fine 

 green, laterally margined and minutely punctuiated with 

 reddish. In the diagnosis given by Miers (op. cit. p. 46), it 

 is stated that the longitudinal median dorsal keel " is obsolete 

 on the terminal postabdominal segment," but this is not so 

 in the specimen I have examined. He also states that the 

 length of the antennae is '* as long, or nearly as long, as 

 the body, without the postabdomen.'" In the example I have, 



