On a, new Vertebrate genus from the northern part of the Tertiary 

 Basin of Green River, October 12th. 



Descriptions of new Extinct Reptiles from the Upper Green River 

 Eocene Basin, Wyoming, October 12th. 



The above essays were distributed widely at the above dates, except- 

 ing that on Metalophodon. 



In an article on Uintatherium mirabile, Prof. O. C. Marsh criticizes the 

 statements made in some of the above essays, denying their accuracy. In 

 reply to such of them as are not frivolous, I would say that I make no 

 corrections of them at present (except one, which I made prior to the 

 appearance of his remarks), but show that his statements were based on 

 species different from those described by me. These he has either not 

 seen or not studied. 



In applying the law of priority in nomenclature, I have endeavored 

 to practice the rules adopted by the majority of students, and which I 

 believe to be founded in justice. They are as follows : 



(1.) Priority reposes on date of publication not on reading of memoirs. 



Note- What is necessary to determine the time at which a discovery of 

 scientific truth is made, is the earliest reliable evidence of such dis- 

 covery. As verbal and written assertion cannot be preserved inviolate, 

 printing is necessary to secure the record from change. The earliest 

 evidence of such printing is that offered by printers, who issue the work, 

 and any person who receives it from them. It is then published. 

 Ordinary books bear such date of publication, whether distributed, sold, 

 or standing on the author's shelves. 



(2.) In order that a specific name be adopted it must be associated with 

 a description of the object to which it refers. 



Note. The necessity of this rule is self evident, since the only value of 

 scientific literature is to convey definite information, which a name does 

 not. Moreover the worst description will generally embrace at least one 

 peculiarity of a species, which will serve to fix the name, but a label, or 

 the specimen itself, may readily be lost or transposed in a museum. 

 Further, in writing descriptions it is necessary to introduce as many 

 points as possible, not only to distinguish the species from those already 

 known, but from those which may in future be discovered ; for it is with 

 these that difficulties chiefly arise. 



(3.) In order that a generic name be adopted, it also must be accom- 

 panied by a description. 



Note. Since naturalists differ to some extent as to what they term a 

 genus, some may be disposed to doubt the expediency of this rule, but 

 its importance to science appears to me greater than in the case of species. 

 In the first place, scientific literature being designed for the communi- 

 cation of exact knowledge, it is essential that its words should represent 

 ideas. The genus is as definite a mental conception as a species, to the 

 scientific, thinker, and in proposing a name, should also express what it 



