Emilio Jorge Power asked about cotypes. The word "cotype" means so many
different things that taxonomists recommend that the word no longer be used
except in a historical context. I think that the term was used mainly from
1880 to 1920, more or less.

Usually, "cotype" is an exact synonym of "syntype", i.e., one of a series
of type specimens on which a species is based, rather than a single type
specimen (holotype) plus a series of other, less important type specimens
(paratypes).

Some authors used "cotype" for the extra specimens of the authors' species
that they traded to other workers for reference, as Gijs pointed out. In
some cases, these are true syntypes; in others, they are not, creating a
taxonomic mess. Some authors seem to have used "cotype" in the sense of
"topotype", that is, a specimen collected from the type locality and
stratigraphic horizon, but not necessarily from the original lot of
specimens collected by the author of the species.

Most confusingly, some workers also considered a cotype to include any
specimen identified by the author of that species. That is, if Smith named
a new species and then identified another specimen at a later time, that
would be a cotype. You can now see why the term had to be abandoned: These
specimens are not type specimens at all. In some cases, they were collected
years after publication of the article naming the species, or even from a
new locality not mentioned in the article, so the author could not have
used them as a basis for his new species.

You can also see why current taxonomic practise emphasizes the designation
of a single type specimen, the holotype, to bear the name of a new species.
The paratypes merely help to fill out the species concept, e.g., by
providing specimens of the other sex or other variations. In the case of
fossils, no complete specimens may exist, but all the parts may be
represented among the holotype and a series of paratypes.

A single museum collection may contain cotypes of different kinds,
including "cotypes" named by the original author or merely labeled later by
someone else. The best thing to do is to check the word usage in the
original publication and in other publications by the same author. In
museum collections, try to recognize the handwriting of the original author
on the labels.

Andrew K. Rindsberg
Geological Survey of Alabama