of the Fishery Board for Scotland. 



Ill 



Fam. Dichhlestiidje. 



Genus Dichelestium, J. F, Hermann (1804). 



Dichelestium sturionis, Hermann. PI. v., figs. 17-24 ; pi. vi., figs. 1-6. 



1804. Dichelestium sturionis, Herm., Mem. Apterologique, p. 



125, Tab. v., figs. 7-8. 

 1837. Dichelestium sturionis, Kroyer, Naturh. Tidsskr., 1st B., 



p. 299, Tab. ii , figs. 5 and 5a ($). 



Description of the Female. — The length of the female represented by 

 the drawing (pi. vi., fig. 1) is 17*8mm (nearly f of an inch). Body 

 elongated and narrow ; cephalic segment nearly as broad as long, widest 

 behind the middle, sides angulated, truncate, and obscurely trilobed in 

 front. Thoracic segments four, first and second subequal, length equal to 

 about half the breadth, and narrowly rounded at the sides ; third seg- 

 ment rather shorter than the one which follows, and each with a shallow 

 transverse suture that divides it into two slightly unequal portions. 

 Genital segment narrow, and about one and a half times the length of 

 the one which immediately precedes it ; the ultimate segment ovate, small, 

 being scarcely half the length of the genital segment. Furcal joints 

 short. Ovisac long and slender (pi. vi., fig. 1). 



Antennules short, slender, and apparently composed of eight subequal 

 joints (pi. v., fig. 17). 



Antennae robust, extremities chelate, and forming powerful grasping 

 organs (pi. v., fig. 18). 



The mandibles resemble those of Caligus or Lepeoptheirus very closely, 

 but differ in having a stouter basal part, and in the long slender 

 rod-like portion being only three-jointed, the last joint being coarsely 

 serrated on the inner edge ( pi. v., fig. 20). 



Maxillse small, two-branched ; primary branch stout, tapering distally 

 and furnished with two slender apical setae; secondary branch very small 

 (pi. v., fig. 21). 



The first maxiliipeds appear to be three-jointed. The first joint, 

 which is large and tolerably dilated, is about as long as the next two 

 combined ; the distal end of the second joint is fringed with short 

 bristles, and the end joint, which is very small, is furnished with a short 

 terminal claw, and a few small marginal spines are shown in the drawing 

 (pi. v., fig. 22). 



The second maxiliipeds, short, very robust and strongly chelate (pi. v., 

 fig. 23). 



The thoracic legs are short and stout. The first and second pairs are 

 two-branched. The branches of the first are indistinctly two-jointed, and 

 the outer branches are furnished with a small spine on the outer distal 

 angle of the first joint, while the end-joint bears five moderately stout 

 spines on its rounded extremity; the inner branches bear each two 

 terminal spines (pi. vi., fig. 3). The second pair are rather more dilated 

 than the first, and both branches are similarly armed (pi. vi., fig. 3). 



The fourth pair is composed of a single uniarticulate branch in the 

 form of an elongated lamelliform plate which bears a few minute teeth 

 round the distal end (pi. v., fig. 24). 



The male, which resembles the female, but is considerably smaller, 

 being scarcely half an inch in length, and the genital segment is also 

 proportionally shorter (pi. vi., fig. 2) ; there is also a difference in the 

 second and fourth pairs of thoracic legs, as shown in the drawing (pi. 

 vi., figs. 5 and 6). In other respects the male is very similar to the 

 female. 



