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BISCAYAX PLANKTON. 



Part XII.— The OSTRACODA. 



Btj G. Herbert Powler, B.A., Fh.D., F.L.S. 



(Plates 16-27.) 



Eead 3rd December, 1908. 



Contents. Page 



I. Introduction 220 



Comparable aud Xon-comparable Hauls . 221 



Manipulation 221 



The difficulty of linking together successive Stages 223 



The argument from constant association 223 



The mathematical relation between different Stages : Brooks's Law 221 



Conchcecia imbricuta as an example , 221 



II. Systematic Part 227 



" Linked " Species 227 



Halocypridae 228 



The " Groups " represented 228 



Cypridinidoe 257 



III. Developmental Part 257 



Halocypridse 259 



Cypridinida; 279 



Herrick's records of Homarus americamis 279 



Measurements of Carcinus mcenas 2S0 



General course of the development 281 



IV. Faunistic Part 282 



The difficulty of determining the lower limit of Species 282 



Halocyprida; 283 



Cypridinidaj 296 



The Vertical Distribution of Ostracoda as a whole 29() 



Suggested zone of diminished sinking-velocity 297 



Explanation of Plate 27 298 



The Vertical Distribution of individual Species 300 



Definitive Observations 300 



The Vertical Diurnal Oscillation of the Epiplankton 302 



Supposed movement of ConcJuecia curta 303 



Simultaneous and consecutive Hauls 305 



Haul 27 a and Open Vertical Nets 305 



V. Miscellaneous Notes 308 



Proportion of Males to Females 308 



The Death-rate 309 



The occurrence of closely allied Species in the same water 310 



VI. General List of Species by hauls and depths 311 



SECOND SERIES. — ZOOLOGY, VOL. X. 38 



