Description of Two New Species of Staurastrum

Abstract

ABSTRACT (Read before the Dublin Natural History Society, on Friday, June 3d, 1859; extracted from the ‘Natural Histmy Review and Quarterly Journal of Science,’ for Oct. 1859.) In these days of cancelling from our lists, and their consolidation with others, of numerous species, or reputed species, in the various walks of natural history,—and this, no doubt, in many cases, with much reason,—it may appear unjustifiable rashness and temerity on my part to come forward for the purpose of describing the following two new forms to be added to our lists of Desmidiaceæ. But in a more extended point of view, in regard to what is a species and what is not, it seems to me that naturalists are prone to err in one of two directions: they either restrict the number of species in their lists within too narrow limits, or inordinately increase their number by giving a name and specific rank to almost every variation which they encounter. On the one hand, because, between two hitherto recognised distinct, but allied species, there are occasionally found forms, as it were intermediate, connecting them, it is assumed that these two original forms must necessarily make but one species. On the other hand, those naturalists might possibly be not wanting who would feel inclined to consider not only the two original, but also one or several of those intermediate forms, as themselves species. Both extremes, as it seems to me, may be wrong. Might it not be expected to be the case that the limits of variation of each of the two original species, so nearly allied, might, so to speak, so touch each other at the margin, as to seem to unite them together, and give rise to the assumption, always plausible, but perhaps not always correct, that one of the original species could (and does), by a series of transitions, pass into the other ? If any one species become modified, is it not to be expected that the characters of the most nearly allied form, and not those of one remote in affinity, will be those which, to a greater or less degree, it will be likely to simulate? Under this hypothesis, the two original forms would still justly be considered true and distinct species—in contradiction to the opinion of the former class of naturalists —while the forms intermediate would be but variations (perhaps but of a temporary or local nature), some derived from one species, some perhaps from the other, and could by no means be looked upon as true species—in opposition to the views of the latter class of naturalists. I do not mean to intimate, when a hitherto acknowledged species is rejected, that I imagine the step always to be an erroneous one, for he who successfully demolishes the spurious claims of a mere book-species does science a good service; but it seems to me that what I have tried to express is a state of things, the possibility of the existence of which, by those who are anxious to suppress species, may sometimes be lost sight of or ignored.