(?) _B. pelagicum_, Günther—Myotomes 36 + 16 + 15: Honolulu, Gulf of Manaar, South Indian Ocean. Genus 2. _Asymmetron_ (Andrews, 1893). With uniserial (right) gonads and asymmetrical metapleura. _A. lucayanum_, Andrews—Myotomes 44 + 9 + 13: Bahamas, Maldives, Zanzibar. _A. caudatum_ (Willey)—Myotomes 40 + 9 + 11: Louisiade Archipelago. _A_. (_Heteropleuron_) _bassanum_ (Günther)—Myotomes 45 + 16 + 14: Bass Straits, Australia. " _cingalense_ (Kirkaldy)—Myotomes 39 + 16 + 8: Ceylon. " _cultellum_ (Peters)—Myotomes 32 + 10 + 10: Torres Straits, Australia, Ceylon. " _maldivense_ (F. Cooper)—Myotomes 45 + 16 + 12: Maldive Archipelago, Zanzibar. " _hectori_ (Benham)—Myotomes 53 + 19 + 12: New Zealand. {138}Thus sixteen species have been described, of which the three under _Branchiostoma_ placed after square brackets, seem to be merely varieties of _B. lanceolatum_, and _B. nakagawae_ is probably identical with _B. belcheri_; while it is a question whether _Asymmetron caudatum_ is more than a variety of _A. lucayanum_, thus leaving eleven or twelve species that seem fairly well characterised. The exact positions of the two marked (?), viz. _B. elongatum_ and _B. pelagicum_, cannot be determined in the absence of fuller descriptions of these species. [Illustration: FIG. 90.—Sketch-map showing geographical distribution of the Cephalochordata. + indicates _Branchiostoma_; o indicates _Asymmetron_.] The list above, and the map (Fig. 90), give some indication of the geographical distribution of the group, and show that, although the few species are widely distributed over the shallow waters of the globe, most of the records lie between 40° N. and 40° S. latitudes. In fact the group is mainly a tropical one, and is most abundant in the Indo-Pacific region. The crosses indicate records of species of _Branchiostoma_, and the circles those of _Asymmetron_ (including _Heteropleuron_); the latter are confined to the Indo-Pacific seas, with the exception of _A. lucayanum_ from the Bahamas—one of the numerous cases of interesting similarity between the marine faunas of the East and West Indies. FISHES (EXCLUSIVE OF THE SYSTEMATIC ACCOUNT OF TELEOSTEI) BY T. W. BRIDGE, Sc.D., F.R.S. Trinity College, Cambridge; Mason Professor of Zoology and Comparative Anatomy in the University of Birmingham {141}CHAPTER V THE SYSTEMATIC POSITION AND CLASSIFICATION OF FISHES In the first chapter of this volume it was pointed out that the Craniata, of which the Fishes form a subordinate group, is the last of the four principal divisions into which the Chordata are divided. The animals included in the first three, viz. the Hemichordata, the Urochordata, and the Cephalochordata, have already been dealt with in the earlier chapters, and it now remains for us briefly to consider the diagnostic characters of the Craniata, and then, more in detail, the organisation of the Fishes.