PEEFACE. XXxi 



300 copies ; in a few cases but 100 copies were issued. They have mostly- 

 appeared in advance of the number of the serial which contains them, owing 

 to the long intervals at which the latter were or are issued. Thus the Pro- 

 ceedings of the American Philosophical Society were, up to a recent date, 

 published but once in six months, and those of the Academy of Natural 

 Sciences three times in the year. In some instances the Paleontological 

 Bulletins have not appeared in any serial. In the earlier part of my inves- 

 tigations the reading of the proofs of these and other papers was sometimes 

 intrusted to other persons, owing to my absence from Philadelphia while 

 conducting explorations. These persons at times allowed important typo- 

 graphical errors to escape them, and in a few instances introduced alterations 

 of the text, for which I wish to disclaim responsibility. This experience 

 led me to avoid such confidence thereafter, so far as practicable. 



The literature of the Paleontology is given under the head of the 

 separate divisions of the subject in which it appropriately falls. 



4. Rules of Nomenclature. — I have adhered to the laAv of priority, 

 as generally understood, in the use of names both in the biological and 

 stratigraijhical aspects of the subject. I take this opportunity of noting 

 what appears to have been at times forgotten by a few students of verte- 

 brate paleontology — although fully recognized by biologists generally — that 

 a name, unaccompanied by a definition or a precise reference to an existing 

 definition, has no status in scientific nomenclature. A word so introduced 

 is meaningless, and cannot be used, because that which it represents is 

 unknown. Thus, names of classes and orders which refer only to popular 

 definitions, such as "flesh-eaters," "insect-eaters," "whales," "worms," &c., 

 have no scientific existence. These divisions of recent animals having been, 

 however, by this time, well established by true analysis, the names pro- 

 posed for extinct groups which are now being discovei'ed claim our 

 attention.* The progress of paleontology has been retarded by the publi- 

 cation of numerous names, supposed to refer to family and generic divisions, 

 which are not accompanied by descriptions or by any statement of the reasons 

 why their author has created them. Characters of the species desci'ibed 



*See Proceedings Americjm Pliilos. Society, 1873, p. 73. Report U. S. Geol. Survey Terrs., 4to, 

 II, p. 113. Report of Lieut. G. M. Wheeler, U. S. Geogr. Surv. W. of 100 Mer., IV, Pt. II, p. 148. 



