| OCR Text |
Show 12G MR. A. S. WOODWARD O N [Feb. 21, tainly not lessened by current advance, for Boas has lately sbov most conclusively1 that the pulmonary artery is homologous throug out the vertebrate series. 2. Pala.ontological Contributions to Selachian Morphology. By A. S M I T H W O O D W A R D , F.G.S., F.Z.S., of the British Museum (Natural History). [Received January 17, 1888.] I. On the Lateral Line of a Cretaceous Species of Scylliidae. It has long been known that the canal investing the sense-organs of the "lateral line" in Selachian fishes attains, as a rule, to a considerably higher stage of development than in the Chimaeroids. While in the latter the canal is merely an open groove, supported by a series of incomplete ring-like dermal calcifications, in the former it assumes a tubular character, opening externally by a row of small orifices, either in its own roof, or through short secondarily developed diverticula. Only two undoubted exceptions to this rule appear to have hitherto been placed on record. The living Echinorhinus is shown by Sol-er2 to have the lateral line in the form of an open groove, though this apparently is not supported by any minute calcifications ; and very similar is the lateral line of Chlamydoselachus, as described by Garman3. The supposed Liassic Selachian, Squaloraja, may also be assumed to have exhibited a similar condition of this organ, the small half-rings originally supporting it being very clearly seen in several fossils recently described before this Society 4, and agreeing in every respect with those met with in Lschyodus and Chimcera. Both of the first-named genera, however, are of a comparatively primitive character, and Squaloraja shows several other marks of resemblance to the Chimaeroids, so that the fact is not unexpected. But I have lately observed suggestive traces of a similarly embryonic lateral line in a most specialized modern type of Selachian ; and as this appears to be an unlooked-for novelty, it may be deemed worthy of a brief note. The Shark in question is a small fossil species, discovered in the Upper Cretaceous strata of Mount Lebanon, Syria, and provisionally assigned by Pictet and Humbert' to the genus Scyllium, under the 1 "Ueb. d. Arterien bogen der Wirbelthiere," Morpholg. Jahrb. vol. xiii. 1887, p. 115. See also ibid. vol. vii. p. 488, and vol. viii. p. 169. 2 B. Solger, ' Neue Untersuchungen zur Anatomie der Seitenorgane der Fische,' Archiv mikr. Anat. vol. xvii. (1880), p. 96. 3 S. Carman, " Chlamydoselachus anguineus, Carm., a living species of Clado-dont Shark," Bull. Mus. Comp. Zool. Harvard Coll. vol. xii. no. 1 (1885), p. 3. 4 Smith Woodward, ' Note on the Lateral Line of Squaloraja ' P Z s' 1887 p. 481. 6 F. J. Pictet et A. Humbert, 'Nouv. Rech. Poiss. Foss. Mont Liban,' p. Ill, pi. xviii. figs. 2-4. |
