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Show 1890.] FIN-SKELETON OF BATOID FISHES. 687 has gone already), those Batoids which remain would fall into two great series-one including the Rhinobatidce, Raiidce, Trygonidce, and most probably the Myliobatidce, which might be provisionally termed the Batoidei veri, as distinguished from the Torpedinidce or Batoidei non veri. Jaekel has failed to recognize one character of especial interest at the present juncture, viz. the presence in many Batoids of a vestigial (sixth) pair of gill-slits. These are disposed lineally with the functional ones and immediately below (ventrad of) the coracoid cartilage. Parker refers to them in Raia nasuta as "looking like an obliterated sixth pair of gill-slits." I fail to see that any other interpretation is possible, and their position and relationships appear to me to warrant the conclusion that the pectoral girdle of the Plagiostomi has, with its related fins, undergone a translocation forwards proportionate to the shortening up of the branchial apparatus by suppression from behind. VI.-The Pectoral Fin-Skeleton and Affinities of the Liassic Squaloraja polyspondyla. My friend Mr. Smith "Woodward, in his excellent paper on this fish1, seeks to associate it with the Sharks and Rays (p. 537), and he would create for its reception the family Squaloraiidce of the Selachh Tectospondyli. H e figures and describes the pectoral fin-skeleton with perfect accuracy, and he regards the anterior of the two basal cartilages which support it as (/. c. p. 536) either " the coalesced pro- and mesopterygium" or "mesopterygial, with a minute indistinguishable propterygium at its proximal angle." In this I believe him to be mistaken. He bases his conclusions, as need hardly be said, upon analogy to the living forms ; but on appeal to them another, and to m y mind more forcible, comparison may be instituted. I have previously attempted to show2 that the paired fins of the Chimseroids are destitute of a mesopterygium, and that Mivart was right in regarding the two-jointed ray of the anterior border of their pectoral fin as a propterygium. Very shortly after the reading of Mr. Smith Woodward's paper, I had the good fortune to examine his specimens; the conclusion that the pectoral fin of his fish was that of a Chimseroid forced itself upon me at the time ; and as all subsequent consideration has the more fully persuaded me that this is so, I avail myself of the present opportunity of recording m y belief. It is, unfortunately, impossible to say whether the propterygium of Squaloraja was or was not segmented ; its posterior border appears to have been thickened and keel-like throughout its proximal region, and examination under a lens reveals the presence of an interspace between the ridge in question and the base of the metapterygium. The Chima)roid metapterygium differs from that of all known Sharks in its gradual increase in depth from behind forwards, and i P. Z. S. 1886, pp. 527-538. 2 P. Z. S. 1887, p. 23. 46* |