200 THALLOPHYTA. [CH. 



recently been determined by Mr Lake^ as corresponding to that 

 of the Wenlock limestone. This species and iV^. Storriei are 

 both Silurian examples of the genus. It is possible, as Barber 

 has suggested, that the specimens described under these two 

 names should be referred to one species. The specimens found 

 by Hicks were small and imperfectly preserved fragments : 

 Etheridge has given a full description of their structure, and 

 Barber has subsequently examined the material. The pre- 

 servation is not such as will admit of any very precise specific 

 diagnosis ; the fragments are correctly referred to Nematophycus, 

 but their specific characters cannot be clearly determined. 



Solms-Laubach^ has described some fragments of another 

 species of Nematophycus from the Devonian rocks of the Lower 

 Rhine. His specimens are chiefly interesting as extending the 

 geographical range of the genus, and as affording examples of a 

 curious method of preservation. The specimens obtained were 

 small fragments, flattened and very dark brown in colour. The 

 tubular elements consisted of an external membrane of black 

 coal, enclosing a central core of dark red iron-oxide. On 

 burning the fragment on a piece of platinum foil the coal 

 composing the wall of the tubes was removed and the deep-red 

 casts of the tube-cavities remained ^ The investigation of the 

 structural characters of this imperfect material was conducted 

 by reflected light. Under certain conditions, when it is im- 

 possible to obtain thin sections for examination by transmitted 

 light, it is possible to accomplish much, as shown by Solms- 

 Laubach's work, by means of observation with direct light. 



The last species to be noticed is Nematophycus Ortoni 

 recently described by Penhallow. There are no concentric 

 rings of growth, no radial spaces and no smaller hyphae in the 

 tissues of this type of stem. In longitudinal section, the tubes 

 show occasional local expansions of the lumen which Penhallow 

 compares with the ' trumpet-hyphae ' of some recent brown 

 algae. No actual sieve-plates or transverse walls have been 

 detected, but the general appearance of the tubes is considered 



1 Lake (95) p. 22. ^ Solms-Laubach (952). 



3 A similar method of fossilisation has been noted by Eothpletz in the case 

 of the Lower Devonian alga Hostinella. [Eothpletz (96) p. 896.] 



