VII] NEMATOPHYCUS. 193 



reasons for this determination were afterwards shown by Oar- 

 ruthers to be erroneous. Dawson thought he recognised pits 

 and spiral thickenings in the walls of the tubular elements, 

 as well as pointed ends in some of the latter. The spiral 

 markings were in reality small hyphal tubes passing obliquely 

 across the face of the wider tubes, and the apparent ends of the 

 supposed tracheids were deceptive appearances due to the fact 

 that the tubes had in some cases been cut through in an oblique 

 direction. In 1870 Carruthers^ expressed the opinion that 

 Dawson's Prototaxites was a " colossal fossil seaweed " and not a 

 coniferous plant. The same author'-' in 1872 published a full 

 and able account of the genus, and conclusively proved that 

 Prototaxites could not be accepted as a Phanerogam ; he 

 brought forward almost convincing evidence in favour of 

 including the genus among the algae. The name Prototaxites 

 was now changed for that of Nematophycus. Carruthers com- 

 pares the rings of growth in the fossil stems with those in the 

 large Antarctic Lessonia stems, but he regards the histological 

 characters as pointing to the Siphoneae as the most likely 

 group of recent algae in which to include the Palaeozoic genus. 

 We may pass over various notes and additional contributions 

 by Dawson, who did not admit the corrections to his original 

 descriptions which Carruthers' work supplied. In 1889 an 

 important memoir appeared by Penhallow' of Montreal in 

 which he confirmed Carruthers' decision as to the algal nature 

 of Prototaosites ; he contributed some new facts to the previous 

 account by Carruthers, and expressed himself in favour of 

 regarding the fossil plant as a near ally of the recent Lamin- 

 ariae. The next addition to our botanical knowledge of this 

 genus was made by Barber^ who described a new specific type of 

 Nematophycus — N.Storriei — found by Storrie in beds of Wenlock 

 limestone age near Cardiff. Solms-Laubach^ in a recent memoir 

 on Devonian plants, recorded the occurrence of another species 

 of this genus in Middle Devonian rocks near Grafrath on the 

 Lower Rhine. Lastly Penhallow', in describing a new species, 



1 Vide 'Academy' 1870, p. 16. ^ Carruthers (72). 



3 PenhaUow (89). ^ Barber (92). 



s Solms-Laubaoh (95^). « PenhaUow (96). 



s. 13 



