GENERIC TYPES WITH SPECIAL REFERENCE TO GRASSES 249 
Upon the selection of types have been separated and arranged, and 
the type species selected according to certain general principles that 
will be set forth in the present paper. Types have been selected for 
proposed genera even though those genera may not be accepted as 
valid, because a non-valid name is referred as a synonym according to 
the identity of its type species. 
Certain definitions and principles are the basis of the work here 
presented. 
The type species of a genus determines the application of the 
generic name. 
In any combination or division of groups the genus, however 
limited, must include the type species. 
The type species is the species or one of the species which the 
author had chiefly in mind when the genus was established. We may 
often be justified in assuming that a certain species is the basis for a 
generic idea because of the fact that the author has figured this one or 
by the fact that he actually examined, or was more familiar with, a 
particular species. Sometimes a careful reading of the generic descrip- 
tion makes it evident that the author based this description upon a 
particular species even though more than one species was included in 
the genus. 
A change of name or a substitution of one name for another does 
not change the type. 
The type is determined upon the basis of facts given with the 
original publication of the generic name. These facts may sometimes 
be interpreted by previous or subsequent historical data. 
In a large number of cases it is easy to determine the type species 
directly, with results acceptable to all. There are, however, a con- 
siderable number of cases in which a more or less arbitrary selection 
must be made and in which the judgments of competent persons will 
differ as to the species selected. In the present paper space permits 
only a summary of results. 
The generic names investigated number 255. These may be 
classified as follows: 
1. The type species has been designated. Total 8. 
2. Type not designated. 
a. Monotypic genera, those in which only one species was 
mentioned at the time of the original publication. Total 150. In 
these monotypic genera the single species is indicated in a variety of 
ways. 
