From H. E. Strickland 15 February 1849
The Lodge | Tewkesbury
Feb 15. 1849
My dear Darwin
When I proposed to use Lepas for Balanus, it was owing to my ignorance that Lepas was properly a name of the pedunculate division. In order to have some kind of rule to go by in subdividing genera, it is necessary to trace out the original type-species, on which, like the lineal descendant of an ancient family, the original estates privileges & title must be for ever entailed. That is the theory, but it happens unluckily that a type-species is a modern idea— Linnæus & his immediate successors considered all the the species in a genus as free and equal, and no more thought of making one species the “type”1 than a Yankee would think of making his eldest son the head of the family.
But as in our modern practice we find that a type-species is a very useful, or rather an essential, idea in the subdivision of genera, we are obliged by a kind of fiction to assume that all genera, Linnæus’s included, have a type-species. There are 2 ways of doing this, one by invariably adopting the first species in the list as the type, the second by determining from etymological or historical sources, the most appropriate species to bear this honour. The former plan is based on fact & is unattended with trouble, hence it has been uniformly followed in Gray’s Genera of Birds.2 The 2d plan is frequently based on opinion, & involves a laborious research into ante-Linnæan authors. Nevertheless an exclusive adherence to the former plan often produces gross & intolerable absurdities (such as calling the Snipes Numenius & the Balearic Cranes, exclusively, Grus, &c because they happened to stand first in Linnæus’s list of species.). I therefore consider that where we can get clear proof from classical or ante-Linnæan authorities as to the particular species or group to which any generic name properly belongs, such species should be considered as the type; but where no such clear proof exists, then the first species in the list of the author who first defined the genus is to be taken as the type— Now I, in my last letter, not knowing the history of the word Lepas, followed the last principle, but as you state that old authors used it only in a pedunculate sense, of course L. anatifera is the type of Lepas, Linn. & accordingly Lepas restricted, should, as you propose, supersede Anatifera, Anatifa, &c.3
Respecting Lepas aurita; as Olfers in 1814 made it the type of Conchoderma, so it must for ever remain, be the limits, & consequently the definition, of Conchoderma, what they may. Olfers might have made another genus contemporaneously or subsequently of L. vittata, or he might have been unacquainted with such a species,—that is quite immaterial. Oken had no business to give a new name to a genus which included another man’s type-species.4
Of course you will understand that by type-species I only mean a conventional distinction, referring only to words, not to things; and like human titles, only used as a matter of convenience. Nature knows no more of type-species or “typical groups” than she does of Dukes and Marquesses. Swainson indeed, & other Quinarians talk very mysteriously about “types” as if the latter got their coronets from Nature & not from Man, but all that appears to me to be fudge.5
Yours very truly | Hugh E Strickland
Clarifies the notion and use of type-species and applies it to CD’s problem with Conchoderma.
Please cite as
Darwin Correspondence Project, “Letter no. 1226,” accessed on 30 September 2016, http://www.darwinproject.ac.uk/DCP-LETT-1226