50 THALLOPHYTES, BRYINAE. 



tion, are considered by him to be of doubtful character, and I do not know 

 them from personal inspection. The question whether Chordophyceae, 

 Crossochorda, Gyrochorda and also Phyllochorda may be tracks of animals 

 has been already fully considered. Whether the Silurian Bilobites, Dekay 

 (Cruziana, d'Orb.) is of the same nature I am unable to determine. Two 

 elaborate monographs on these fossils by Saporta 1 and Delgado 2 have 

 recently appeared, and these contain also a complete account of the ex- 

 tensive and scattered literature. Both authors are at great pains to prove 

 that the remains are those of Algae, but they will scarcely induce the 

 botanists to take this view; they have equal claims to be regarded as 

 Holothuriae, Ctenophorae, sponges or anything else we may please to call 

 them. As regards the Arthrophyceae, it has been already shown that 

 Nathorst is wrong in referring the type of this group to the tracks of 

 animals. The Taenidiae 3 I have never examined ; Nathorst considers that 

 they are the tubes of worms. The Dictyophyteae (Dictyophyton, Uphan- 

 taenia) are referred by Hall 4 to sponges. 



The genus Oldhamia 5 from the Cambrian slates of Ireland, which has 

 been supposed to be the oldest of all vegetative types and appears only as 

 a delicate wrinkling of the surface of hard slate beds, is now regarded by 

 F. Romer c and indeed by most observers as the result of simple pressure or 

 some similar purely mechanical cause. Saporta 7 too would seem not to 

 consider these markings to be of vegetable origin, or he would not have 

 failed to mention them as the oldest types of the class of Algae. With 

 Scolithus, Haldem., Vexillum, Rouault, Eophyton, Torell, and Granularia, 

 Sap. 8 , we come at last to shapeless objects of quite indefinite character. 

 Eophyton has been already discussed ; Vexillum is produced every day in 

 the soft mud of our ponds, where local currents are interfered with by 

 floating impediments, such as branches of trees and the like. 



The Chondriteae, which occur in all formations and when found in the 

 older deposits generally go by the name of Bythotrephis, are remarkable 

 for their copious branching. Innumerable figures of them are given in the 

 works of Heer 9 and Saporta 10 . The latter says of them and of countless 

 other forms 11 : c In fine, we have no hesitation in referring the whole of 

 this assemblage of primordial types to one of the groups of inferior Algae, 

 that of Siphoneae; this group has arisen from a very remarkable differen- 

 tiation of a thallus, which though branched continues to be unicellular, &c.' 

 Nothing further need be added to this statement from the botanist's point 

 of view. Nathorst of course regards them as traces or tubes of worms, and 



1 de Saporta (12). 2 Delgado (1). 3 Heer (3), t. 67. 4 Hall (2). 



5 Zittel (1), vol. ii, p. 60. " F. Romer (1). 7 de Saporta (3). * de Saporta 



(4), vol. i, t. 12. Heer (3). w de Saporta (4), vol. i. " de Saporta (3), p. 93. 



