I. THE NATURE OF EDESTUS AND RELATED FORMS. 



In that rich treasure-house of anatomical information, Owen's Anatomy or 

 Vertebrates, under the caption of the Skull of Osseous Fishes, we read as follows: 

 "It is truly remarkable, writes the gifted Oken, what it costs to solve any one 

 problem in Philosophical Anatomy. Without knowing the what, the how, and the 

 why, one may stand, not for hours or days, but weeks, before a fish's skull, and our 

 contemplation will be little more than a vacant stare at its complex, stalactitic form." 



If such bewilderment is possible, nay rather, if it be the common experience 

 of students in their initial attempt at homologizing the bones of the head in recent 

 vertebrates, how much more intricate is the problem confronting the palseozoologist 

 when surveying only fragmentary remains, and deprived of all save the most meagre 

 points of orientation? And yet it not unfrequently happens in paleontology that, 

 through some fortunate discovery or other, a fresh clue is found, or a new point of 

 view obtained, and that which was formerly obscure suddenly becomes illuminated. 

 The what, the how, and the why no longer elude our grasp, and once enigmatical 

 structures or organisms assume their proper place in an orderly system. 



A striking example of this nature is furnished by the history of Edestus and 

 kindred fossil remains occurring in the Carboniferous and Permian rocks of Europe, 

 North America, and Australia, concerning which much diversity of opinion has existed- 

 Occurring as they do singly, and always in a detached condition, these objects have 

 been most frequently looked upon as selachian fin-spines, although their correspond- 

 ence with dental structures has been patent to nearly all writers. Originally re- 

 garded by Leidy ('56, p. 414) as part of a fish-jaw segmented like that of Lepidosteus, 

 and compared by L. Agassiz (see E. Hitchcock, '56, p. 229) with the rostral prolonga- 

 tion of Pristis, the remains of Edestus were later classed' by Leidy ('57, p. 301) and 

 Owen ('61, p. 123) with dermal defences of sharks or skates, and referred to a posi- 

 tion in advance of the dorsal fin. The resemblance between their segmented char- 

 acter and that of the pectoral fin-spines of Protosphyrsena ("Pelecopterus") was 

 pointed out by Cope ('75, p. 244) and by H. Woodward ('86, p. 120). Newberry ('88, 

 p. 120) suggested that the fused segments of Edestus may correspond to a series of 

 spines such as occurs upon the tail in some species of Trygon, and in furtherance of 

 the same general idea, Dean ('98, p. 67) supposed them to have had a metameral 

 origin in the anterior muscles of the trunk, from which position they "may have mi- 



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