. Catalog of fossil fishes in the Carnegie Museum. Fishes, Fossil. 324 MEMOIRS OF THE CARNEGIE MUSEUM. contains within itself certain potentialities of continuous variation. It is charged, so to speak, with a complex of latent characteristics. One set of these is that which terminates in an elongated tubiform snout, the other in the development of a peculiar kind of dermal armor, including a long and slender dorsal fin-spine. In the tube-snout evolutionary series the gradual elaboration of these two sets of characters, which may be supposed to be resident potentially in Gasterosteus, goes hand
. Catalog of fossil fishes in the Carnegie Museum. Fishes, Fossil. 324 MEMOIRS OF THE CARNEGIE MUSEUM. contains within itself certain potentialities of continuous variation. It is charged, so to speak, with a complex of latent characteristics. One set of these is that which terminates in an elongated tubiform snout, the other in the development of a peculiar kind of dermal armor, including a long and slender dorsal fin-spine. In the tube-snout evolutionary series the gradual elaboration of these two sets of characters, which may be supposed to be resident potentially in Gasterosteus, goes hand in hand; and thus we find that Centriscus has both a tubular snout and is provided with dermal armor and a well-developed dorsal fin-spine. But in the rostrate series one of these sets of characters is suppressed, no tubular snout being developed. The second group of characters which was potentially present in Gasterosteus is developed in precisely the same fashion as in the Centriscoids, with the result that in Rhamphosus we find a body-armor paralleling that in Centriscus, and a remarkably similar dorsal fin-spine. The divergence in forms with reference to the splitting up of the original complex of characters might be illustrated by the following scheme: Rhamphosus Fistulariids T Aulostomids I Urosphen I Aulorhynchus Amphisile T Centriscus. Gasterosteus Family Rhamphosid^ Gill {emend.). Solenichthyes with Gasterosteus-like form of body, the anterior vertebrae discrete and not elongated, about twenty-two (eight abdominal and eighteen caudal) vertebrae in all; dermal plates on the nape and shoulder-region only; a single, elongate dorsal spine arising from the hinder end of the nuchal armature. Mouth small, and placed as in Gasterosteus, but the upper portion of the head produced in an elongate rostrum. Ventral fins subthoracic, the second dorsal and anal remote and opposite. 2. Rhamphosus rastrum (Volta). (PL XLIV, Figs. 1-3). 1796. Uranoscopus rastrum G. S. Volta, Ittiolit.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfishesfossil, bookyea
