GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



191 



we have examples of families, each of which preserves a characteristic ground-plan of skull structure, 

 more or less divergently modified in accordance with considerable differences in the jaws and in the muscle 

 areas and associated with wide differences in the dentition. Having many such instances in mind the 

 writer felt that the fundamental agreement in skull structure between Ada pis and Notharctus indicated 

 a common origin of the two subfamilies, that from an evolutionary and tax(5nomic viewpoint the agree- 

 ment in skull structure outweighed, for tlie moment, the divergence in the dentition, as it does in the 

 families above cited. For the rest, when Di'. Stehlin states that: "Welches audi der Grund jener Struc- 

 turdivergenzen sein mag, sie sind nun einmal Thatsache, haben eine bestimmte Zeit gebraucht, um sich 

 herauszubilden und sind bei der Reconstruction des Stammbaumes zu beriicksichtigen," he formulates 

 an unassailable verity; and when he proclaims that "Die Divergenz der Stammlinien muss unter alien 

 Umstanden bis an den Zeitpunkt zuriickgeschoben werden, wo die Divergenz der Gebissstructuren 

 deutlich wird," he will encounter opposition from no one. 



Dr. Stehlin's Concept of "Family" 



The many striking differences in the dentition and skull of the Adapinte and I^Totharctinffi which 

 have been noted in the prececUng pages will no doubt be judged by many authorities to justify Dr. Stehlin's 

 arguments (1912, pp. 1287, 1290; 1910, pp. 1518-1520, 1538-1540) for keeping the Adapida and Noth- 

 arctidse as distinct families. But, before discussing this subject, it will be necessary to consider the 

 different viewpoints of Dr. Stehlin and the present writer with regard to the content of the term "family" 

 and with regard to the general aims and best methods of zoological classification. 



To Dr. Stehlin a "family" of Eocene mammals apparently means a small group of extinct genera, 

 founded chiefly on dental characters, but having in common such a strongly marked pattern of the whole 

 dentition that there can be no doubt that they are more closely related to each other than to any other 

 genera; the genera and species of such families are recorded during successive formations of the Eocene 

 of Europe and North America, but their pateontological connections with modern families are not known. 

 Dr. Stehlin refuses to assign to these families any genera as to the affinities of which his minute analysis 

 has raised in his own mind the slightest doubt. He evidently aims to have his "families" represent an 

 irreducible residuum, remaining after the elimination of the deceptive resemblances brought about by 

 analogous evolution, and purged so far as possible of all hypothetic speculation and mental restoration 

 of defective evidence. He develops at great length the vast complexity and difficulty of the problem 

 of the Eocene Primates, sets apart a few small groups as ultimate categories, leaving the rest "incertse 

 sedis," and virtually declares the futility of further efforts, except as to minor problems, until the Paleo- 

 cene records of A.sia shall become available. 



Dr. Stehlin appears to regard any more comprehensive groups, such as Dr. Wortman's "Neopithe- 

 cini" and the writer's " Tarsiif ormes " as mere "Rubriken" (1916, p. 1541), hypothetical and ephemeral 

 guesses of no enduring value ; although at the end of his memoir he himself speaks provisionally of vague 

 superfamily assemblages, which he calls "Entwicklungsherden," designating them not by systematic 

 names but by numbers and by the name of the continent wherein they are supposed to have originated. 



Value of the "Linna^an System" of Classification 



Dr. Stehlin's general attitude toward the so-called Linnai-an system of classification and toward the 

 synthetic or interpretative categories which he calls "Rubriken" is stated in the following passage: 



