How to … Choose a type for a name of a new genus
The type of a name of a genus or of any subdivision of a genus is the type of a name of a species (Art. 10.1).
When designating or citing the type of a generic name, the species name alone is sufficient (but see below). The term "type species" is sometimes seen, but this should be avoided because a species, which is a taxon, cannot be a type (taxa have names, names have types).
When choosing a type for a name of a new genus, you may choose a validly published name of any species that falls within your circumscription of the genus. There is no requirement to choose the first-described species.
In general, it is good practice to choose a species that is "typical" for the genus. This is because if you choose a very atypical species and the genus is subsequently split, the segregate taxon containing the type is more likely to be small, requiring more new combinations for the species in the other segregate genus or genera.
When designating a name of a new genus, you should also cite the type of the relevant species name. Be aware that some older species names may not yet have a type (because they were published without a holotype). If this is the case, you should designate a lectotype or neotype for the species name.
For more information, see Chapter 7 How to designate a type in The Code Decoded.