Since some pages of your valuable magazine are occasionally devoted to the description and illustration of “Gems from Private Collections,” allow me to offer a drawing and some observations on Spirifera convoluta, Phillips, one of the most remarkable of our British carboniferous spirifera, and which will serve at the same time as a small supplement to the paper I published in the eleventh number of The Geologist.

At page 35 of my “Monograph” I described Sp. convoluta as a distinct species, but subsequently I thought that it might, perhaps, be a very transverse or exceptional condition or variety of Sp. bisulscata, Sowerby.

Experience teaches us that individuals of the same species may assume great differences in shape; that a Spirifera, for example, which in its normal condition is about as wide as long, may at times exceed these proportions very considerably in one or the other direction, and that we are often too prone to seize upon similar variations as pretexts for the creation of so termed species.