of the Fishery Board for Scotland. 



179 



slightly produced middle portion of the posterior end of the genital 

 segment, while on each side of it is a minute tubercle representing the 

 posterio-lateral processes so characteristic of species of ChondracantJtus 

 nnd Braclnella. 



The specimens of Anchorella stellala which I have observed were found 

 adhering to the scales near the bases of the pectoral and ventral fins, 

 especially those of the pectorals, of the hake. It is interesting to note 

 that Krbyer found his specimens of this Anchorella also on the same 

 species of fish. 



In concluding for the present these notes on the copepod parasites of 

 fishes, I may mention one point which has been of some interest to me in 

 the course of my study of the structural details of the various species I 

 have had the privilege to examine. A cursory glance over the plates of 

 figures which accompany these notes shows that alaiost all the species 

 that have been recorded arrange themselves naturally into three distinct 

 groups by the structure of their mandibles. In the group to which 

 Caligus and Lepeophtheirus belong the mandibles are for the most part 

 long and slender ; their apex has usually a slight inward curve, and the 

 inner edge of this curved portion is minutely serrated; the mandibles in 

 this group are also usually composed of several more or less distinct joints. 



In the second group represented by Ghondracanthus the mandibles are 

 large and falciform — somewhat like a broad-bladed scimitar — with one 

 edge, and sometimes with both edges, fringed with setae or teeth. 



In the third group represented by Bracliiella and Lernaipoda the 

 mandibles assume a cleaver-like form, and the anterior third part, more or 

 less, of the inner margin is nearly straight and armed with teeth usually 

 coarse, and sometimes irregular in shape. Other peculiarities of structure 

 — as for example, that of the antennules, characteristic of certain groups — 

 may also be observed by anyone who cares to devote a little time to the 

 study of these interesting organisms. 



I will now proceed to notice briefly a few crustacean parasites of fishes 

 belonging to some of the groups that have come under my observation, 

 and my notes will, as in the preceding part of this paper, refer principally 

 to Scottish species. 



(1) Branchiura. 



Argulus foliaceus, Linn. 



A few years ago this curious little entomostracan was found to be very 

 common on the greyiing, Thymallus vulgaris, in the upper waters of the 

 Clyde. So much were these fishes infested by the little parasites that 

 they were blamed for being the cause of the unhealthy appearance which 

 these fishes at this time had assumed. A friend secured a number of the 

 parasites and sent them to me, and promised to try and obtain some 

 more. It happened, however, that within the next few days a heavy 

 rain set in and flooded the river, and he was thus prevented from securing 

 other specimens; and when the weather moderated he found that the 

 Argulus had all disappeared, and that the fish had assumed a more 

 healthy appearance. 



Argulus foliaceus has also been taken on the three-spined stickleback, 

 Gasterosteus aculeatus, in the Union Canal near Edinburgh, by Miss 

 Janet Carphin, who kindly presented me with a few specimens. 



Several species of Argulus have been described by Continental writers 

 on parasitic Crustacea, but A. foliaceus is the only one I know of as 

 occurring in Scottish waters. 



