of the Fishery Board for Scotland. 



187 



elongate secondary branches of the fifth pair of thoracic feet, and the 

 elongate caudal furca, in which the exterior marginal seta has a 

 position nearly midway between the base and apex of each furcal 

 segment 



Cyclops vernalis and Cyclops bisetosus were also observed in a few of 

 the lochs examined. C. bisetosus is a distinctly smaller Cyclops than the 

 other ; in structure C. bisetosus seems to occupy an intermediate position 

 between C. bicuspidatus and C. vernalis. 



Cyclops languidus and Cyclops nanus. — The first of these two Copepods 

 was only observed in Loch Doon, but the other has been obtained both in 

 Loch Doon and Loch Lomond, thus indicating by the difference in the 

 altitude and position of these two lochs that it may have a moderately 

 extensive distribution in Scotland. Dr. Schmeil is inclined to regard 

 both these Cyclops as forms of Cyclops vernalis. Cyclops nanus is a very 

 small species with eleven-jointed antennules ; several specimens carrying 

 ova were observed amongst the representatives of this species in Loch 

 Doon. With regard to C. languidus, the character that first attracted 

 attention was the structure of the antennules, which were found to be 

 sixteen-jointed. 



Cyclops macrurus. — This appears to be a moderately scarce species. 

 It was observed in only two of the series of lochs under consideration — 

 viz., Loch Arklet and Loch Leven. 



Cyclops atfinis was observed only in the Dhu Loch (close to Loch 

 Lomond). It appears to be rare in the lochs of Scotland. 



Cyclops phaleratus. — This species is recorded from only two of the 

 present series of lochs — Forfar Loch and Duddingston Loch. Ova- 

 bearing specimens of all these species have been observed and examined. 

 In the preparation of lists such as these it is often preferable to defer 

 recording a species till ova-bearing specimens can be obtained, as there is 

 always more or less risk of error in the discrimination of immature forms. 



Diaptomus gracilis has already been referred to as one of the more 

 generally diffused and common of the fresh-water Copepoda, but two other 

 species of Diaptomus have been observed which are less common, and 

 these may now be referred to : — 



Diaptomus laciniatus. — Loch Doon is the only loch in which this species 

 has been obtained. If it be safe to judge of its distribution by what has 

 been observed in regard to its occurrence in that loch, D. laciniatus seems 

 to be more affected by seasonal changes than some other of the fresh- 

 water species. A number of specimens were obtained in a gathering 

 collected in September 1897, but in those collected in December 1897 

 and March 1898 not a single specimen was observed. When subsequently 

 in the month of July following the loch was again tow-netted, Diaptomus 

 laciniatus was found to be moderately common. Professor G. S. Brady 

 has recorded a Diaptomus from Ireland which may probably belong to the 

 same species, and, curiously enough, the loch in which this Irish Diapto- 

 mus was discovered is also called Loch Doon. This species is quite 

 distinct from any other British Diaptomus by having the last two 

 segments of the thorax curiously produced at the sides. 



On Plate XIII., figure 1 represents an adult female ; figure 2 shows one 

 of the fifth pair of thoracic feet of the same specimen ; figure 3 represents 

 one of the fifth pair in the male ; and figure 4 shows the last three joints 

 of the right antennule of the male. 



