. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 86 bulletin: museum of comparative zoology. designated. It is a well-established principle of nomenclature that in cases like this, or as between names the equal pertinency of which may- be in question, " jiret'erence shall be given to that which is open to least doubt " (A. O. U. Code, Canon XVII.). As a matter of fact, when these two "species" were united by St. John and Worthen in 1883, some slight doubt was expressed as to their identity, and the authors very properly chose for their common des
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 86 bulletin: museum of comparative zoology. designated. It is a well-established principle of nomenclature that in cases like this, or as between names the equal pertinency of which may- be in question, " jiret'erence shall be given to that which is open to least doubt " (A. O. U. Code, Canon XVII.). As a matter of fact, when these two "species" were united by St. John and Worthen in 1883, some slight doubt was expressed as to their identity, and the authors very properly chose for their common designation that which was founded on the most perfect specimen, and hence was open to least doubt, namely, C. gracillimus. By this decision the spine figured in Plate XIII. Figure 3 of the Illinois Palseon- tology. Vol. II., was definitely established as the type-specimen, and the only question is whether it actually belongs to Ctenacanthus, or should be removed to Acondylacanthus as was proposed by Newberry in 1889. The latter author rests his claim upon a worn, im- mature, and distorted specimen, now in the Museum of Columbia University, and very much inferior in point of presei'vation to the spine figured by St. John and Worthen in Vol. II. of the Illinois Palaeontology, to which no reference is made by Newberry. The correctness of St. John and Worthen's deter- mination is confirmed by several additional specimens which have come under the writer's observation, all Fig. 12. ^f which show tuberculated cost£e, and the absence Ctenacanthus gracil- of this character in Newberry's spine is probably due to abrasion. One example in particular, from the St. Louis limestone, and belonging to the Museum of Comparative Zoology, exhibits the finer ornamenta- tion very distinctly in its proximal portion {cf. text- figure 12) where the tubercles are seen to be small, stellated, and rather widely spaced in proportion to the extreme fineness of the costae. Just as C. xiphias (St. J. and W.),
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