Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/206

 and Lepidodendron, we are not justified in uniting Cyclostigma to Lepidodendron.

These are the grounds which have led me to treat the Cyclostigmata, Knorrioe, and Lepidodendra of the Yellow Sandstone of South Ireland as separate species. I have formed my opinion from careful research upon the specimens sent me from Tallowbridge and Kiltorkan ; and I think I have found better and sharper characteristics for the two species of Cyclostigma than have yet been known ; for, indeed, in some degree, satisfactory representations of each of them have been till now wanting. I do not know any transitions which would establish a connexion of these different plant-remains ; therefore I have no right to unite species made not by myself but by others. I will not dispute the possibility of the connexion, as I know well the gaps in our knowledge of the ancient floras ; but proofs of it must first be afforded before we can accept it.

I have left out of consideration the Stigmarioe of Kiltorkan and Tallowbridge, as the position of the Stigmarioe is especially doubtful. The few specimens which I have received from Ireland have large, tolerably close-set scars ; and near them lie root-fibres like those present in Stigmaria ficoides. This form agrees with the specimens I have received from Bear Island and figured in pl. xii. of my ' Bear- Island Flora.' The Stigmarioe are now generally regarded by palaeontologists as the roots of Sigillaria. Schimper, however, unites one form with Knorria imbricata, Geinitz, and another with Lepidodendron Veltheimianum. So long as it is not determined to which plants these rhizomes belong, we must give them under separate names.

EXPLANATION OF PLATE IV.

Fig. 1. Fragment of a branch of Lepidodendron Veltheimianum, Sterub., from Tallowbridge ; 1 b, a portion, magnified.

2. Branch of Cyclostigma minutum, Haught., from Kiltorkan ; 2 b, a portion, magnified.

3. Portion of the stem of Cyclostigma minutum, Haught., from Kiltorkan.

4. Branch of Cyclostigma kiltorkense, Haught., from Kiltorkan ; 4 b, portion, magnified.

5. Cyclostigma kiltorkense, Haught., from Kiltorkan; a, fragment of the stem ; b, a portion of a, magnified ; c, fragment of a branch.

6. Knorria acicularis, Gopp., from Tallowbridge.

Discussion.

Mr. Carruthers was glad that he had made the observations which he did on Prof. Heer's former Paper, as it had caused the Professor to give the reasons on which his opinions were based. He was doubtful whether the success which had attended Prof. Heer's determination of species from leaves justified the application of the same principles to mere stems. He could not accept the difference in size or distance of leaf-scars as a criterion of species, inasmuch as they were merely the result of the difference in the age and size of the parts of the plants on which they were observed.