. The Paleozoic fishes of North America [microform]. Paleontology; Fishes, Fossil; Paléontologie; Poissons fossiles. 38 PALEOZOIC FISHES OF NORTH AMERICA. Comparatively few cartilaginous fishes of the present epoch are pro- vided with even dorsal spines; and nont?, so far as known, carry spines on the pectoral fins. But in the Mesozoic and the Paleozoic ages the Elas- mobranch fishes were much more generally provided with spines, and it 18 not too much to suppose that this tendency to the development of organs of defense should be exhibited in spines appended to the anterio paired fins. We hav
. The Paleozoic fishes of North America [microform]. Paleontology; Fishes, Fossil; Paléontologie; Poissons fossiles. 38 PALEOZOIC FISHES OF NORTH AMERICA. Comparatively few cartilaginous fishes of the present epoch are pro- vided with even dorsal spines; and nont?, so far as known, carry spines on the pectoral fins. But in the Mesozoic and the Paleozoic ages the Elas- mobranch fishes were much more generally provided with spines, and it 18 not too much to suppose that this tendency to the development of organs of defense should be exhibited in spines appended to the anterio paired fins. We have, in fact, positive evidence that some of the sharks of the Carboniferous age did carry pectoral spines, Severalof the species of Gyra- canthus, for example, are now gener- ally conceded to have been pectoral spines. This is shown by their want of symmetry, which proves that they were not set on the median line, and by the fact that they are worn off in various degrees, as though used as organs of locomotion on the sea bottom or shore. A series of spines of Gyracanthus formosus, in the cabi- net of Columbia College, show, (1) a slender, complete, evidently young spine ten inches long and unworn, (2) a large spine nine inches ' jng, of which the summit is obliquely and smoothly worn off where five-eighths of an inch in diameter; (3) the base of an old and very large spine worn away nearly to the end of the ornamented portion. I have silso shown in another part of this memoir that the spines called Physonemus Altonensis by St. John and Worthen were certainly apj)endage8 to the pectoral fins. This was first suspected from their obvious want of symmetry, and was finally proved by finding complete specimens buried in soft shale, in which *ae cleft of the convex margin is occupied by the base of a broad pectoral Flo. 1. Spinrfior MadiaiTnoanthiisperacutaa,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabili
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