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Show 1903.] IN THE ‘ CHALLENGER ' COLLECTION. 53 specimens, on 22 of the species in question, 15 of which were established by Bate himself. Furthermore, he refers Petcilidium Bate, Sciacaris Bate, Acetes H. M.-Edw., and Lucifer Yaugh. Thomps. to his family Sergestidae; of Lucifer he describes two species, but the genus must be more thoroughly studied than has hitherto been done before the examination of the 1 Challenger ' specimens ; Scicicaris Bate has one species, which is only a larva of a Sergestes, and the type seemed to be wanting in the Museum ; of A cetes, Bate had no specimens; and Petalidium is mentioned below. Of Bate's 31 species of Sergestes only 6 are really mature forms, 25 being larvae. Special attention has been paid to the adult specimens preserved in the Museum and enumerated by Bate; on two of these specimens I have established two new species, and besides I add notes and some drawings to the representations of Bate. Unfortunately nearly all the specimens of rare and especially interesting species were very much mutilated. Our present knowledge of the adult species of Sergestes of the Atlantic fauna is far from complete, but yet we are acquainted writh so many species that it was possible for me in my earlier paper either to refer the Mastigopus-forms examined to the mature species, or to describe the older larval stages and sometimes the black-eyed but still immature forms, so that they can be recognized with certainty and referred to the mature forms when these are discovered in the future. All the Atlantic larval forms from the 1 Challenger ' seen by me have now been referred in a similar w^a.y. But many larvae established by Bate as valid species of adult or sub-adult animals have been secured in the Pacific. Our knowledge of the mature stage of the species living in that vast ocean is still rudimentary ; and I have therefore not been able to refer the larvae of three of Bate's species to any species established on adult specimens. Bate's types of his species established on larval forms are often either defective or very young, wherefore I thought it of little use to describe and figure them again; but I have generally added some notes on their affinities, and sometimes also a few corrections to his descriptions. When the Pacific has been moderately well explored by further expeditions, many adult forms and their larval stages will be discovered ; and a future student of the group will then be able to refer at least some of the larvae, which I cannot interpret, to their adult forms. To the young larvae described by Bate as species of Mastigopus I pay no attention at a ll: the types seem to be lost. I think it convenient first to deal with all the ‘ Challenger ' species in the same consecutive order in which they are described in Bate's Report; then to put together some results of the investigation ; finally, to mention more fully the luminous organs in Sergestes challengeri, n. sp. In order to abridge the descriptions, in the following pages- as in xoy earlier paper-I noake use of some abbreviations :- |