DICHELESTIUM OBLONGUM. 107 



reflexed and furnished with a small apical claw which 

 can be folded inwards so as to impinge against a 

 rounded knob and thus form a tolerably powerful 

 grasping-organ. Mandibles somewhat like those 

 of OaliguS except that the basal part is rather 

 stouter. Maxillae small, biramose, primary branch 

 stout, tapering towards the distal end, and bearing 

 two slender apical seta3 ; secondary branch very small. 

 The first maxillipeds with the first and second joints 

 of nearly equal length, but the first is more robust ; end 

 joint very small and bearing a few short spines and 

 setae. Second maxillipeds short, robust, and furnished 

 with stout terminal claws. Thoracic legs short and 

 stout, and the first and second pairs biramose. Both 

 rami of the first pair indistinctly two-jointed, the 

 proximal joint of the outer ramus having a small spine 

 on its outer distal angle while the end joint has five 

 spines : all moderately stout, on its rounded apex ; 

 the inner ramus, which is shorter than the outer, 

 carrying two terminal spines. The second pair 

 similar to the first but the outer branch rather stouter 

 and the spines shorter ; the inner branch also propor- 

 tionally rather shorter. The fourth pair one-branched 

 and each branch consisting of a single uniarticulate, 

 lamelliform plate, rather longer than broad, with a few 

 minute prickles round the distal end. ' Length 17 to 

 18 mm., but varying somewhat. 



Male. — The male bears a close resemblance to the 

 female, but is considerably smaller, and the genital 

 segment is proportionall} r shorter. In the second 

 pair of thoracic legs the inner branch is very short 

 and broad, and bears on its outer aspect a small flat- 

 tened plate. The fourth pair are also proportionally 

 shorter and broader. Length about 13 mm. 



'Habitat. — Parasitic on the gills of the sturgeon, 

 Acipenser sturio. On a sturgeon captured atPolperro, 

 Cornwall, in 1867 (.1. -1/. Norman). On a sturgeon 

 captured about sixteen miles S.E. by E. of Aberdeen 

 in December 1904 (Dr. Alex Bowman). On a sturgeon 



