22 ANNALS OF SCOTTISH NATURAL HISTORY 



Three visits were made to this part of the Ythan during 

 the past summer, twice in July and once in August, and the 

 results, briefly set forth in the sequel, were fairly satis- 

 factory. 



The bridge which spans the river at the village of Ellon 

 is said to be the limit to which the influence of the tide 

 extends, but it is not till one gets below Waterton that any 

 difference in the Entomostracan fauna of the river begins to 

 be observed. It may be stated further that the river for 

 some distance both to the east and the west of the bridge 

 does not present conditions very favourable to Entomostracan 

 life ; it is only when we get beyond the railway viaduct on 

 the one hand and below Waterton on the other that good 

 hunting ground is met with. A little above the viaduct the 

 land bordering the Ythan on the south side assumes the 

 form of a flat, low-lying meadow, and here, there is what 

 looks like part of an old bed of the river, and through which 

 the water may still find a channel when in flood. I visited 

 this place on I3th July, and at that time this old channel 

 had practically no connection with the river except at its 

 lower end, and the water it contained, being undisturbed, 

 seemed to be a very suitable habitat, and, along with a few other 

 places in the neighbourhood, yielded no fewer than forty-two 

 species of these minute crustaceans. It was noticeable, how- 

 ever, that though there was great variety, the individuals of 

 each kind were comparatively few ; it was in marked contrast 

 to what is sometimes observed in lochs and ponds, where 

 myriads of individuals will sometimes be met with, but with 

 very little variety as regards species. Several of the species 

 obtained have not before been recorded for. the county. The 

 part of the river examined in August was the north shore, 

 from about half-way down the Waterside Road to a little 

 beyond the confluence of the Burn of Forvie. Near the 

 ferry, between Denhead and the Kirkton of Logie-Buchan, 

 is a considerable amount of marshy ground, intersected by 

 a burn and a few ditches. Here some moderately rare fresh- 

 water species were found, while near and beyond the mouth 

 of the Forvie several interesting brackish-water Copepoda and 

 Ostracoda were collected. The number of species obtained 

 on this occasion was thirty-nine, only two of which belonged 



