172 phoceedings op inE geoxogicil society. 



and l/epidodendron, wo are not justified in uniting Cydostirjma to 

 Lepidodendron. 



These are the grounds which have led me to treat the Ci/clostir/- 

 onata, Knorrue, and Lepidodendra of the Yellow Sandstone of South 

 Ireland as separate species. I have formed my opinion from care- 

 ful research upon the specimens sent me from Tallowbridge and 

 Kiltorkan ; and I think I have found better and sharper character- 

 istics 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 jStipnarice of Kiltorkan and 

 Tallowbridge, as the position of the jStif/marice 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 pi. xii. of my ' Bear- 

 Island Flora.' The Stigmarice are now generally regarded by palaj- 

 ontologists as the roots of Siglllaria. Schimper, however, unites one 

 form with Knorria imhricata, Geinitz, and another with Lepido- 

 dendron Yeltheimianum. 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 Lepidode7idron Veltheimianum, Sterub., from 

 Tallowbridge ; 1 6, a portion, magnified. 



2. Branch oWyclostigmaoninictum, Haught., from Kiltorkan ; 2Z», a portion, 



magnified. 



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



4. Erancli of Cyclostigma kiltorJcense, Haught., from Kiltorkan ; 4:b, jiortion, 



magnified. 



5. Cyclostigma JciltorJccnse, Haught., from Kiltorkan; a, fragment of the 



stem ; h, a portion of «, magnified ; c, fragment of a branch, 



6. Knorria acicularis, Gropp., from Tallowbridge. 



Discussion. 



Mr. Cabettthees 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 dif- 

 ference in size or distance of leaf-scars as a criterion of species, inas- 

 much 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. 



