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This is particularly the case in the morę aenescent species which are with difficulty separated from the ripples which sur-round them. Swimming quietly on still water they are easily seen but on the approach of danger the school commences an intricate dance breaking the water into a thousand ripples amongst which it is well-nigh impossible to follow the move-ments of an individual, This difficulty is increased by their habit of making short dives, The swerving dance, the glitter of the disturbed water and the constant disappearance and reap-pearance of the individuals is so confusing that it is doubtful that even the most swift and keen sighted of enemies could effect a capture.

Phylogeny and C 1 a s s i f i c a t i o n.

Two able workers have recently expressed their opinions about the phylogeny and evołution of the group. MELVILLE H. Hatch has madę a very careful comparative study of the external anatomy of the genera, both recent and fossil, and has expressed his opinions in several papers¹). OCHS, whose know-ledge of the systematics of the group is unrivalled, has also considered the subject²). These workers hołd almost diametri-cally opposed views. My own view differs from both of them but is closer to that of MELLVILLE Hatch than of Georg OCHS.

The group is smali and compact and comprises about 500 known species. It was well established in the Miocene. In the Oligocene a form Palaeogyrinus strigałus Shal. existed which appears in some ways, to be intermediate between the Dyłis-cidae and the Gyrinidae. The insect was robust and might be

1

1)    Hatch, 1925, Phylogeny and Phylogenetic Tendencies of Gyrinidae. Papers Michigan Acad. Sci, Art, and Lett, Vol V, pp. 429—467.—Hatch, 1926, The Morphology of the Gyrinidae. Ibid. Vol VII, pp. 311—350, Pis, XX—XXIV.—Hatch, 1927, A Revision of Fossil Gyrinidae. Buli, Brooklyn Ent, Soc, Vol, XXII, pp, 89—96, pl, VII,

2

)    O c h s, 1926—27. Die Dineutini. Ent, Zeitschr, Frankfurt a, Main, Vol. XXXX pp, 61—74, 112—126, 129—140, 190—197 —O c h s, 1930, Gyrinoidea. Cat. Indian Insects, Part 19, pp, I—II, 1—39,