ON BOSMINIDiE, MACROTHRICIDiE, ETC. 355 



published since Dr. Baird's work, except in cases where it seemed 

 necessary, either for the purpose of correcting some mistake or 

 of showing the precedence of some name, to indicate an earlier 

 authority who has noticed the species. 



By far the most valuable papers which have recently been 

 published on the Cladocera are those of Gr. 0. Sars. The writ- 

 ings of this author are in all cases marked by evidences of the 

 greatest care and the closest accuracy of details. His general 

 arrangement of the Sub-order, as given by him in the first part 

 of his " Gorges Perskvandskrebsdyr," is far more satisfactory 

 than any that has preceded it ; and it has therefore been followed 

 by us in this memoir. 



Of the thirty-three species of Cladocera here described, only 

 fifteen will be found recorded as British in Dr. Baird's work ; 

 the number of our species has thus been more than doubled. No 

 less than twenty-eight out of the thirty-three species have been 

 found by us within the confines of the Counties of Northumber- 

 land and Durham. The remaining five which have not as yet 

 been observed within this district are Macrothrix rosea, Jurine ; 

 Lathonura rectiroslris, Midler; Bosmina Coregoni, Baird; Anchis- 

 tropus emarginatus, Gr. 0. Sars ; and Lynceus reticulatus, Baird. 

 The first of these has been found in Lochmaben Castle Loch, 

 Dumfriesshire, and in some of the small lakes of Connemara ; the 

 second is only known in our Islands to inhabit Lough Bollard, 

 Connemara; the third only Lochmaben; the fourth has only been 

 observed in the Paisley Canal, near Glasgow; while the last has ap- 

 parently not been noticed since it was first described by Dr. Baird. 



Sub-order. CLADOCERA. 



Div. CALYPTOMEEA, G. 0. Sars. 



Body enclosed in and completely covered by a vaulted shell, 

 which forms two valves below, within which the body moves 

 freely. Mandibles truncate at the inferior extremity. Maxillae 

 distinct, movable, furnished with geniculated setae or spines. All 

 the thoracic somites distinguishable from each other and double, 

 united by longitudinal and transverse sutures. 



