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Show 128 MR. WOODWARD ON SKLACHIAN MORPHOLOGY. [Feb. 21, pubic cartilage in its median portion is straight and narrow, but becomes slightly broader and is angularly bent backwards at about one fourth of its total length from either extremity. From each angulation in front there projects forward a very long tapering pre-pubic process, rightly interpreted as such by Sir Philip Egerton in his original description of the fossil; and immediately in advance of the point of attachment of the basal cartilage of the pelvic fin on each side another larger process is seen to extend laterally. This is almost or quite as broad as the median portion of the pubic cartilage itself, and is directed outwards, without apparent tapering, to a distance equal to the entire transverse extent of the complete pubic element, when it bends backwards almost at right angles, and is half Pelvic cartilage of Cyclobatis oligodactylus, from the Chalk of Mount Lebanon, Syria. op, basal cartilage of pelvic fin; il, iliac process; pb, pubic cartilage ; p.pb, prepubic process. as long again, though rapidly narrowed to a point. This remarkable process was described by Egerton as the " proximal digit " of the pelvic fin, while Mr. J. W . Davis has recently3 hazarded the suggestion that it " may have been the basal portion of a clasper." As, however, no sutural line can be observed at the origin of the cartilage, and as it is sometimes seen to be dorsally placed with respect to the other structures, there cannot be much doubt that it is the homologue of the well-known process named the iliac. The enormous proportions of these processes in Cyclobatis appears at present inexplicable, the prepubic equalling no less than one sixth the entire length of the disk. No known Selachian, so far as I am aware, exhibits pelvic-arch processes of equal relative size, and in the living Trygon these are comparatively insignificant or absent 2. 1 J. W. Davis, " Fossil Fishes of Chalk of Mount Lebanon " Trans "Rov Dublin Soc. [2], vol iii. 1887, p. 492. ' ' y' 2 In the figure of the skeleton of Trygon given by Agassiz (' Rech. Poiss Foss.' vol. iii. pi. n. fig. 1), a large ascending process is shown connecting the pelvic cartilage with the vertebral column. This must be an artist's error J |
