ON SOME FRESH AND BRACKISH WATER ENTOMOSTRACA 161 



Some of these pools, which were examined in September 

 last year, and again in February and May of the present, are 

 more or less brackish, being situated very little above the 

 high-water level of ordinary spring tides. The Cladocera 

 observed in them, though moderately abundant, exhibited 

 very little variety, and the predominating form was the 

 almost ubiquitous Chydorus spliczricus (P. F. Miiller). One of 

 the species collected last September was Ilyocryptus sordidus, 

 Lievin, a species which has a wide distribution in the 

 smaller lochs and tarns of Scotland, but which, when I first 

 began the study of the fresh-water Entomostraca, was 

 scarcely so familiar to students as it now is. Another 

 Cladoceran recently found in the pools on the King's Links 

 is the rare Macrothrix liirsuticornis, Norman and Brady, 

 but only five or six specimens were observed. This is the 

 largest of the three British species of Macrothrix^ and the 

 finest of my specimens measure almost a millimetre in length, 

 which is practically identical with the size (-^ of an inch) 

 given by the Rev. A. M. Norman and Dr. G. S. Brady in 

 their description of the species. 1 In this species the dorsal 

 edge of the carapace is smooth, but " the most marked 

 character consists in the anterior antennae, which are some- 

 what club-shaped, sub-truncated, rounded at the extremity, 

 and, in contrast with the long tentaculiform setae of M. 

 laticornis, are only furnished with fine hairs distributed 

 round their extremity ; but arranged here and there 

 throughout the length of the antennae are tufts or semi- 

 verticils of fine hairs, which are more evident on the anterior 

 margin, but are also present on the sides ; on the posterior 

 margin there are no hairs except near the distal extremity." 

 The only other place in Scotland where this species has 

 been obtained is Loch of Beiton, Unst, Shetland, where it 

 occurred in a gathering collected by Mr. Robert Duthie, 

 Fishery Officer. 1 ' It is of interest to notice that the Loch of 

 Beiton is near the sea and not much above sea-level, and 



1 ' A Monograph of the British Entomostraca belonging to the families Bos- 

 minidce, Macrothricidse, and Lynecidre,' "Trans. Nat. Hist. Soc. Northumb. and 

 Durham," vol. i. p. 10 (separate reprint), pi. xxiii. figs. 6 and 7. 



2 'The Inland Waters of the Shetland Islands,' by Thomas Scotland Robert 

 Duthie, part iii. , " Fourteenth Annual Report of the Fishery Board for Scotland," 

 part iii. pp. 237 and 242, pi. ix. figs. 12 and 13. 



39 D 



