Wesley Thorsson writes:
 
It occurs to me that a number of beginners in taxonomy may be slightly
confused by two terms used in this thread:
 
"group":   as used in genus-group  and  species-group.
 
"later established"  relating to  secondary homonyms.  Does this
indicate that the date of the specific name was later?
 
Aloha
Wes
 
OK. To take them in ascending order:
 
"Species group" includes subspecies, species, and superspecies. The older
terms "variety" and "form" are considered to refer to subspecies, unless
they are clearly below the subspecific level (e.g., if a form is ranked as
belonging to a variety, then the form is infrasubspecific).
 
"Genus group" includes subgenus (section, division, ...), genus, and
supergenus. Terms such as "section" are inserted into the classification
system in cases where needed for clarity.
 
"Family group" includes subfamily (tribe, ...), family, superfamily.
 
Orders, classes, phyla, and kingdoms are not governed by the Code. That's
why we have alternative names for the same classes of mollusks, e.g.,
Univalvia = Gastropoda; Bivalvia = Pelecypoda = Lamellibranchiata.
 
"Later established" means "validly published at a later date". There are a
lot of rules that govern whether a publication is to be deemed as valid and
what its publication date is, and the rules have been modified in
succeeding editions of the Code. It's pretty complex, and taxonomists who
get too involved in the Code sometimes sound more like jurists than
scientists.
 
Andrew K. Rindsberg
Geological Survey of Alabama