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The Structure and Affinities of the Fossil Elasmobranch Fishes from the Lower Carboniferous Rocks of Glencartholm, Eskdale

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Summary.

  • (i.) A new specimen of Ctenacanthus costellatus is described, which shows the teeth, pectoral, pelvic, and caudal fins particularly well. The affinities of the species is discussed, and it is shown that the Ctenacanth sharks occupy a position intermediate between the Cladoselachii and the Hybodonts.
  • (ii.) A new genus of shark, Goodrichia eskdalensis, is described. It is a large member of the Ctenacanths, but has remarkably small dorsal fin spines.
  • (iii.) Tristychius arcuatus is redescribed and its pelvic and caudal regions described for the first time. It is believed that it should not be included in the Hybodonts, but in a distinct suborder, the Tristychii, probably not far removed from them.
  • (iv.) The teeth of Chondrenchelys are shown to be typically Bradyodont in microscopic structure.
  • (v.) The teeth of Oracanthus armigenis and relations of the head spines are discussed, and the dermal denticles and body spines described. The affinities of the Cochliodonts are discussed and a short description of the anatomy of Helodus simplex is given. It is concluded that the Bradyodonts, Edestids, Chondrenchelyda, and Chimæroids form a natural group.
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Ancillary