Yes, here applies Art. 69.3 of the International Code on Zoological Nomenclature:

69.3. Type species by subsequent monotypy. If only one nominal species was first subsequently included in a nominal genus or subgenus established without included species, that nominal species is automatically fixed as the type species, by subsequent monotypy.

(see  http://iczn.org/iczn/index.jsp )

Dear Ronald,

Thank for your answer. I have seen this article of ICZN but as I understood the genus need to be originally established WITHOUT included species, which as not the case. Leontopithecus was created with 3 species in it. But its first subsequent mention had only one of the three in it, while the other two were allocated to another genus.

I think you can consider that case as "subsequent designation"

The original description of Leontopithecus was not without included species, but without a type species designation, which has the same effect of a missing typification of the genus. Therefore I consider Art. 69.3 as effective in this case.

As no type species was included in the original description, we have to rely on the first revising author; he considered the genus as monotypic, which automatically fixes the single included species as the type species of the genus. The other species which were originally included in the genus were not considered as congeneric by the first revising author, so they cannot be treated as potential type species.

If you think that Art. 69.4 applies in this case, you need a thorough examination of Reichenbach's (1836) chapter to decide if there is reason to assume that he designated Leontopithecus leonina as the type species, beyond the exclusion of the other species. In a brief outline of the taxonomy of Leontopithecus, Coimbra-Filho & Mittermeier (1972) indicate that the genus was also revised by Gray (1870), so if Reichenbach (1836) does not qualify as the first reviser Gray (1870) may be used.

The first reviser principle is widely used in the Code. However, there is no need to treat it as obligatory. The stability of nomenclature should always be kept in mind , so even if you find a first usage or type designation that is contrary to this aim, it may be ignored. In such cases I like to remind to the preamble of the Code: "The objects of the Code are to promote stability and universality in the scientific names of animals and to ensure that the name of each taxon is unique and distinct. All its provisions and recommendations are subservient to those ends and none restricts the freedom of taxonomic thought or actions."

Thanks Luis, I think that is indeed the case. Lesson (1840) included only three species, but inside one of the species he included two "variants" (proto-subspecies?).

Ronald, yes i agree that stability must be mantained. In fact, Pocock (1917) designted the type of the genus as marikina (= rosalia), but I thought that maybe Reichenbach made a previous designation.

All the best,

Art. 69.3 is not for such case! It should be under Art. 69.1, type species should be subsequently designated here. If it was not done in some other work yet it should be done now. leonina cannot be considered as a type species of Leontopithecus by act of Reichenbach.