. The Cambridge natural history. Zoology. 138 CEPHALOCHORDATA Thus sixteen species have been described, of which the three under Brancliiostoma placed after square brackets, seem to be merely varieties of B. lanceolatum, and B. ncikagawae is probably identical with B. helcheri ; while it is a question whether Asym- metron caudatwn is more than a variety of A. lucayammn, thus leaving eleven or twelve species that seem fairly well character- ised. The exact positions of the two marked (?), viz. B. elonga- tum, and B. pelagicum, cannot be determined in the absence of fuller descriptions of these
. The Cambridge natural history. Zoology. 138 CEPHALOCHORDATA Thus sixteen species have been described, of which the three under Brancliiostoma placed after square brackets, seem to be merely varieties of B. lanceolatum, and B. ncikagawae is probably identical with B. helcheri ; while it is a question whether Asym- metron caudatwn is more than a variety of A. lucayammn, thus leaving eleven or twelve species that seem fairly well character- ised. The exact positions of the two marked (?), viz. B. elonga- tum, and B. pelagicum, cannot be determined in the absence of fuller descriptions of these species. 40 80 120 160. 3iayi/srcCs Gay^ £slui' londun. Fig. 90.—Sketch-map showing geogi'aphical distribution of the Cephalochordata. + indicates Branchiostoma ; o indicates Asyvimetron. 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""^. 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 Heterofleuron); the latter are confined to the Indo-Pacifio 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 Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harmer, S. F. (Sidney Frederic), Sir, 1862- ed; Shipley, A. E. (Arthur Everett), Sir, 1861-1927. ed. [London, Macmillan and Co. , Limited; New York, The Macmillan Company
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