174 



Part III. — Seventeenth Annual Report 



The total number of Crustacea obtained in, and around the shores of, 

 Loch Doon amounts to sixty-three species, and comprises twenty-three 

 species of Copepoda, ten of Ostracoda, and twenty-nine of Cladocera, to 

 which has to be added Gammarus jpulex. 



The shore gatherings collected in September and March yielded the 

 largest number of species, while the one collected in December gave very 

 poor results ; even the results of the tow-net gatherings collected at this 

 time were disappointing, w r hich was probably owing, in part at least, to 

 the stormy weather then prevailing and to the Hooding of the loch. But 

 while this was "he least successful of the various gatherings collected, 

 it w 7 as the only one in which the rare Maraenobiotus was obtained. 



The number of species of each of the three groups of Entomostraca 

 observed in the various shore gatherings is shown in the formula. 

 Co., Copepoda; Os., Ostracoda; CI., Cladocera. 





Sept. 16, 

 1897. 



Dec. 12, 

 1897. 



March 31, 

 1898. 



July 6, 

 1898. 



Names oi the Groups, . 



Co. Os. C: 



Co. Os. CI. 



Co. Os. CI. 



Co. Os. CI. 



Number of Species in each 

 Group, .... 



12 8 2 



5 0 3 



16 5 12 



10 5 11 



Total Number of Species in 

 each Gathering, 



41 



8 



33 



26 



A number of minnows were obtained in the September gathering, and 

 the contents of several of their stomachs were found to consist chiefly of 

 Cladoceran remains ; those remains that were perfect enough for identi- 

 fication represented at least eight different species. Trout are fairly 

 plentiful in Loch Doon, and fine specimens are occasionally captured. One 

 of the largest has been preserved, and is in the possession of Mr. James 

 Macdonald of the Eglinton Hotel, Dalmellington. 



It appears that extensive deposits of marl exist in Loch Doon ; and, 

 about the time of my visit to the loch in July, advantage had been taken 

 of the water being so low to have some of it excavated. Some of the marl 

 was so pure that when it was dried it closely resembled a piece of chalk 

 both in colour and weight. A sample which I collected, measuring 

 nearly nine cubic inches, weighed scarcely four ounces when dry. It was 

 solid throughout, and exhibited indistinct traces of lamination. It was 

 nearly white in colour, but variegated with light brownish bands. When 

 dissolved in water and carefully examined no remains of molluscan shells 

 were observed ; it seemed to consist largely of a fine whitish mud, in 

 which were numerous Diatomacea and seeds of Chara or Nitella. But 

 the marl varied in purity to a considerable extent ; though of moderate 

 thickness in some places, in others it consisted only of thin layers inter- 

 bedded with dark vegetable matter ; but whether in thin or thick layers, 

 it seemed to be characterised by the absence of Molluscan shells, and thus 

 differed very markedly from the marl observed in Forfar Loch. It may, 

 in the absence of Molluscan remains, be somewhat difficult to determine 

 from what source this marl is derived. A chemical examination of the 

 water at different seasons of the year might probably throw some light on 

 this question. 



