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Part III. — Eighteenth Annual Report 



Habitat. — Our specimens of this species were obtained in the gill- 

 cavity of Trigla gurnardas from the Firth of Forth, the Firth of Clyde, 

 and at Aberdeen Fish Market ; also on Trigla lineata from the Clyde, 

 and on a specimen of Trigla hirundo in the collection of fishes in the 

 Laboratory at Bay of Nigg. 



Genus Lepeophtlieirus, Nordmann (1832). 



The species belonging to this genus are, in their general form, very 

 similar to Caligus, but, as already said, there are no lunulce on the frontal 

 plates, and the palpi are furcate instead of being simple and spine-like. 

 Six or seven species belonging to this group have been obtained on fishes 

 examined by me. 



(1) Abdomen composed of one segment. 

 Lepeophtlieirus pedoralis (Miiller). (PI. V., figs. 26-31.) 



1776. Lernea pedoralis, Miiller, Zool. Dan., p. 41, PI. 



XXXIIL, fig. 7. 

 1850. Lepeopththeirus pedorali*, Baird., Brit. Entom., p. 275, 



PI. XXXIL, fig. 10. 



The* specimen of Lepeophtlieirus pedoralis represented by the figure on 

 Plate V. (fig. 26) measures about five millimetres (one-fifth of an inch) in 

 length ; the cephalic shield is nearly circular ; the last segment of the 

 thorax is large and sub-quadrate, but its lateral margins are very slightly 

 curved ; the abdomen is short, and somewhat constricted near the middle, 

 so that in certain positions it appears as if it were composed of two 

 segments ; the caudal segments are very short. 



The antennae (posterior antennae) are provided with strong terminal 

 hooked claws. The mandibles, which are small and slender, have the 

 inner edge of the distal joint distinctly toothed (fig. 28). The posterior 

 foot-jaws are strong, and they are armed with stout, curved terminal 

 claws. In the sternal fork the branches become dilated in the middle 

 then taper to a point at the end (fig. 29). TDiq palpi are furcate. 



The fourth pair of thoracic feet have the branches two-jointed, and are 

 provided with three terminal setae, and there is also a small seta or spine 

 on the outer distal angle of the first joint. The fifth pair, which consist 

 of small but comparatively broad lamelliform plates, provided with two 

 or three minute terminal hairs, are situated behind the bases of the 

 ovisacs, and are therefore easily missed. 



The male (fig. 27) is little more than half the size of the female, but 

 the cephalic shield is proportionally larger ; the last segment of the thorax 

 is small. In the male antennae the basal joint is rather more dilated 

 than in that of the female, while the terminal claw is smaller and more 

 strongly hooked. 



This is one of the more common and easily identified species of 

 Lepeophtlieirus. The peculiar form of the sternal fork, the small fourth 

 pair of thoracic feet, and the short abdomen seem to be fairly good specific 

 characters. Slight differences in the general form of the animal and in 

 some of its structural details are occasionally observed, especially in 

 specimens from different fishes, such as the plaice and the flounder. 



Habitat. — Found for the most part adhering to the underside of the 

 pectoral fins of plai3e, Pleuronedes platessa, from the Firths of Forth 

 and Clyde, and at the Fish Market at Aberdeen ; on flounders, Pleuronedes 

 flesus, from the Firth of Forth and the Moray Firth ; and on common 

 dabs, Pleuronedes limanda, from the Firth of Forth. 



