. Geological magazine. illee;mesially, they articulate with each other along a portion of theirinternal margins, while externally each comes into contact with _ 1 Described as interoperculum in my Memoir on the Structure of the Palaao-niscidae. I have, however, abandoned that view, and now consider the plate inter-calated between it and the opercidum in such genera as Rhabchlepis to be not a sub-operculum, but merely an accessory element. 2 On the Structure and Development of the Skull in Stm-geons, Phil. Trans,vol. 173 (1881), p. 172. 3 See Stannius, Handbuch der Zootomie der Wiibelthiere, er
. Geological magazine. illee;mesially, they articulate with each other along a portion of theirinternal margins, while externally each comes into contact with _ 1 Described as interoperculum in my Memoir on the Structure of the Palaao-niscidae. I have, however, abandoned that view, and now consider the plate inter-calated between it and the opercidum in such genera as Rhabchlepis to be not a sub-operculum, but merely an accessory element. 2 On the Structure and Development of the Skull in Stm-geons, Phil. Trans,vol. 173 (1881), p. 172. 3 See Stannius, Handbuch der Zootomie der Wiibelthiere, erster Theil, DieFische, p. 53. 254 Dr. R. H. Traquair—On Chondrosteus acipenseroides. the maxilla of its own side for tlie anterior half of its length, behindwhich the margin recedes inwards, the little bone pt. being placedjust where the recession takes place. These plates were recognizedby Sir Philip Egerton as palatine, and are undoubtedly the repre-sentatives of the two plates occupying a corresponding position in. Acipenser, and which, although formerly usually reckoned as pala-tines, are designated as pterygoids by Prof. W. K. Parker.^ Tomy mind it seems to correspond more with the mesopterygoid of otherfishes, and I have lettered it accordingly. Placed at the middle of the outer edge of this last described bone,and articulating both with it and with the maxilla, is a small 1 Op. cii. p. 172. Dr. R. H. Traquair—On Chondrosteus acipenseroides. 255 bone {pt.) which bifurcates posteriorly, one limb being placedalong the middle, the other along the mesopterygoid is the bone which Sir Philip Egerton has interpreted asmaxilla {op. cit. pi. Ixix. 21), but whose true relations are mostclearly seen in a large number of specimens in the British relations are not obscure even in the specimen figured bySir Philip ; but here, as already explained, he unfortunately mistookthe real maxilla for the lower jaw. As the position of this littlebone is about t
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