248 Scientific Proceedings, Royal Dublin Society. 



fig. 2, two distinct genera are represented. Fig. 2« (" Dichotomizing stem 

 of the ordinary size ") of Baily is, he thinks, very like his own Cephalopteris 

 mirahilis from the Upper Devonian Eoeks of Bear Island. In the specimen 

 figured to the right the uppermost primary pinnae appear to him opposite and 

 fertile. Nathorst further regards fig. 2h (" Dichotomizing stem of a larger 

 size ") of Baily, on account of the transverse striaB figured, as a Heterangium 

 or allied genus. 



Though Baily's " type" specimens of Filicites lineatus are not at present 

 forthcoming, there are other specimens of "Linear Plants" in the collections 

 of the Geological Survey, and these I examined, and had in some cases 

 photographed, without venturing to locate them definitely, spite of Nathorst s 

 suggestions. One day, however, Mr. Hallissy, of the Geological Survey, 

 showed me a specimen of a " Linear Plant " he had unearthed from the 

 stores of the Survey, and a very cursory examination satisfied me that the 

 specimen was a fine impression of a Heterangium (PL XX., fig. 1). 



Heterangium Grievii (Willm. sp.), the hest-known species, was described as 

 long ago as 1720 as Fiimaria officinalis, but in 1822 was separated by 

 Brongniart (3) as a Fern under the name Sphenopteris elegans. Brongniart's 

 description is confined to the fragments of foliage he had before him. His 

 fig. 2 shows the dichotomy of the rachis, though he does not call attention to it. 

 He includes in his diagnosis the transverse striation of the rachis, without, 

 however, introducing it into his figure. The fullest account of the external 

 features of S. Grievii is due to D. Stur (4), who was so impressed with the 

 importance of dichotomy of the frond in the Palaeozoic plants that he created 

 a genus Diplothmema, in which he placed a heterogeneous collection of fossil 

 plants with dichotomy of the primary rachis as a distinguishing feature in 

 common. In this genus he placed Brongniart's 8. elegans under the name of 

 Diplothmema elegans. Although Stur speaks of making transverse sections of 

 the stem, he does not describe them, and, in fact, says nothing of the internal 

 anatomy of the plant. On the other hand, he gives an elaborate illustrated 

 account of the external features. His figures are so true that I at once 

 recognized my " linear plant " as the same as his D. elegans. Kidston (5) 

 notes that the transverse striation in H. Grievii occurs in 8. elegans 

 Brgt. and 8. grancUfrons Sauvear. Stur concluded his plant was a Fern, 

 though he rightly rejected Goppert's evidence of the presence of 

 sporangia. 



The most complete account of Heterangium Grievii is given by Scott (6) in 

 his " Studies in Fossil Botany." It is based on the investigation of the 

 anatomy of the plant by Williamson (7) and Scott in 1896, this being a 

 revision of Williamson's investigation in 1873. We learn that Heterangium 



