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Show 1887.] FOSSIL CHLAMYDOSELACHUS. 543 confirmed his opinion at greater length, and stated that the recent fish should be named Didymodus anguineus. Prof. Th. Gill was disposed to consider Chlamydoselachus to stand " nearer the true fishes than do the Sharks proper, not because it appears to be in the line of descent between the two, but because it is nearer the primitive line from which both types have diverged." Thus far he agrees with Mr. Garman, but he dissents emphatically from him in regarding the recent acquisition as a Cladodont Shark, and agrees with Prof. Cope that Chlamydoselachus had a representative in the Carboniferous genus Diplodus or Didymodus, although he does not think that the two can be congeneric. He suggests the name Pternodonta as preferable to the one given by Mr. Garman. A month later, however, Prof. Gill withdrew his adhesion to the Diplodus scheme of affinity ; and he says, " I am convinced not only that Didymodus has no generic or even family relations with Chlamydoselachus, but that it represents even a different order." His objection is founded on the undoubted relationship of Diplodus and Pleuracanthus, and the possession by the former of a large dorsal fin and nuchal spine, of which there is no evidence in the recent fish ; and he concludes that the anatomy of the latter will probably reveal a structure most like that of the Notidanidae, but of a somewhat more primitive type. In 'Science,' May 30th, 1884, Prof. Cope discusses the relationship of Diplodus, Agass., and Didymodus, Cope, and regarding the former as the teeth of the fish bearing Pleuracanthus-sp'mes, states that it must be separated from the genus Didymodus, and that Chlamydoselachus is distinct on account of the different structure of the dorsal fin and the absence of a spine; but that hitherto no Pleura-canthoid spines have been found directly associated with Didymodus (though they are found in the same strata), and consequently, so far as we know Chlamydoselachus, it will not differ from Didymodus. These views were published in greater detail in the July 'Proceedings of the American Philosophical Society of Philadelphia.' And so matters remained until the following September, when Mr. Garman read a paper at a meeting of the American Association for the Advancement of Science, in which he strongly reiterated his views as to its relationship with the fossil Cladodus, with the result that both Profs. Cope and Gill abandoned their positions and accepted the views of Mr. Garman, Prof. Gill still dissenting "from the opinion that the Cladodontidae are related to the Chlamydoselachidse rather than the Hybodontidse." In July 1885 Mr. Garman published a detailed description of the fish in the ' Bull, of the Museum of Comparative Zoology at Harvard College,' vol. xii. no. 1, pp. 1-35, pis. i.-xx., in which he styles it " a living species of Cladodont Shark." Leaving this extremely problematical relationship of Chlamydoselachus to be substantiated or otherwise by future investigation, it is extremely interesting to find that ten years ago a fossil representative of Chlamydoselachus was actually discovered and figured by the late Robert Lawley. The specimen is from the Pliocene heds of Orciano in Tuscany, and is described as verv rare ; the teeth figured are 36* |