Owing to the kindness of the authorities of Dublin Museum, I have been permitted to make a most exhaustive and critical examination of Haliday’s type collection of British Mymaridæ, and though the hand of time and those of others have materially interfered with their original arrangement, the result has been most satisfactory to me. Although one or two of the most interesting types are absent, I have been enabled to re-establish Haliday’s genus Panthus, which certain compilers had, for no apparent reason, ignored. I found two specimens still bearing the old labels, and after long and critical microscopic examination I saw that both were distinct from any others. I applied for and obtained permission to remove the carded specimens, and remount them in Canada balsam. This was successfully done, and on making a photo-micrograph the peculiar generic characters were brought out most distinctly. Some naturalists appear to imagine that a pocket lens will be sufficient to identify these species, but in an insect which is but a fiftieth or an eightieth of an inch long it is of absolute importance that every joint and detail should be examined under the microscope, and the relative proportion of each joint of the antennæ be compared with closely allied species--just as they are with all large Hymenoptera. The curve, too, of the delicate wings is a most important feature which must not be hurried over. This point leads me to speak of the immense superiority of photo-micrographs over drawings of these fairy flies. No matter how exact an enthusiastic naturalist may be in his endeavors, it is a physical impossibility for any one to follow out and reproduce the exact curve of these microscopic wings; and as the flies when properly prepared and “set” in Canada balsam lend themselves peculiarly to photo-micrography, it is wise to take advantage of this. The details can afterward be drawn to a much larger scale. It is my intention to do this with every species which I have collected during the past twenty-five years, and of which I have a very large number, far exceeding those known to science. The illustrations accompanying this short article will, I think, show what exceedingly good subjects the fairy flies are for photo-micrographs. Since Haliday’s arrangement of the British Mymaridæ, elucidated by Francis Walker, no new species have been recorded, the genera numbering eleven, the species, thirty-five, as follows, viz.: _Ooctonus_, four species _Gonatocerus_, five species _Alaptus_, two species _Litus_, one species _Eustochus_, one species _Mymar_, one species _Cosmocoma_, eight species _Caraphractus_, one species _Anaphes_, seven species _Anagrus_, four species _Camptoptera_, one species Of these I have found representatives of all, and a few notes may not be uninteresting to those who desire to search for these fairy flies.