jg GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



ported by the evidence drawn from the methods of evolution or the record of phylogeny. To the student of evolu- 

 tion, the genus represents a certain characteristic portion of the line or field of specialization, and its existence is 

 as definite as that of the species which constitute it. . . As a consequence of the unrestricted play of personal opinion, 

 not infrequently aided by bias or carelessness, present-day taxonomy contains genera of every possible quality. Many 

 of these disappear completely when the test of evolution is applied to them (p. 6). 



In paleontology, more than in neontology, genera are not uniform in differentiation; one stock 

 will vary but little while another will do so extensively. The genera with but one or a few species 

 will practically take care of themselves, but in those with a great number of species it is desirable to 

 name all the determined genetic lines, since evolution is the -process and taxonomy the method of 

 marking the phylogenetic lines of descent. 



It is clearly recognized that the making of new genera is purely a matter of personal judgment at the present 

 time. . . There is no general agreement as to criteria, methods, or results, and the importance of evolution as 

 the one safe guide is rarely if ever considered. A knowledge of the genus as a whole, especially when it 

 includes exotic species, is too often lacking, and little or no thought is given to the phylogeny of the genus and its 

 sections in relation to genera of the same evolutionary stock. . . It would seem desirable to make rather more of 

 sections as records ... of specialization within the generic stock (pp. 8-9). 



PALEOECOLOGY 



The paleontologist should study his specimens and species primarily in the light of the field to 

 learn their environmental and biotic relations, since the strata of their entombment are the habitats 

 of fossils. We hold with Clements" that the habitat is 



the motive force in the life processes of plants and animals, both as individuals and as communities. . . Ecology 

 deals primarily with processes and is inherently and universally dynamic . . . quantitative in method, beginning with 

 the habitat in which measurements are relatively simple, and running through individual and community responses 

 in which they are difficult (p. 369). 



As paleontologists we should, therefore, be primarily interested in the habitat of fossils and of 

 our faunas, since organisms are "the end forms of responsive processes." In other words, it is seem- 

 ingly the environment in the main that brings on the organic responses seen in the development and 

 evolution of fossils; accordingly the paleoecology and the time factor of our faunas should be con- 

 sidered in addition to the morphology, in the making of species and genera. 



In paleontology we have, it is true, but a small part of the whole of the habitat or of the bios, 

 and therefore it is "puzzling to understand how the demands of ecology can be met in a field where 

 processes have ceased. The readiest answer, and a fairly complete one, is afforded by the princtple 

 of uniformity of processes [italics ours], the use of which has made modern geology possible" 

 (p. 370). Accordingly we paleontologists can learn much from the ecologists, but most from the 

 entombing strata and the associations of the fossil faunas. 



In the paleoecology of marine faunas, the main factors in conditioning the local biotas are the 

 interrelations of temperature, currents, nearness to shore, and nature of sea bottom; depth, chemical 

 content, and clarity of water; prevalence of bottom-living flora, nature of floating life, presence of 

 oxygen as food, penetration of sunlight, and interaction of life. 



HOMCEOMORPHY 



What has long been known as "parallel development" has had but scant notice among Anierican 

 students of brachiopod ancestry, Beecher'" being about the only one to pay attention to this principle 

 of mimicry of outer form; among the ammonites, however, the factor has been used a great deal 

 since its introduction by Alpheus Hyatt and its later acceptance by J. P. Smith, In Europe, Buck- 



" Scope and Significance of Paleo-ecology. Bull. Geol. See. America, vol. 29, 1918, pp. 369-374. 



^''C. E. Beecher, Some Correlations of Ontogeny and Phylogeny in the Brachiopoda. Amer. Nat., vol. 27, 1893, 



pp. 599-604. 



