JErFREY. — NATURE OF SOME SUPPOSED ALGAL COALS. 281 



ticularly striking. Figure 17, Plate 2, shows two upper tetrads some- 

 what highly magnified. In the lower of these the alveolar structure 

 of the walls of the spores is specially prominent, the plane of section 

 being particularly favorable. There seems to be no reason for doubt 

 that here we have to do with the structures from Scotch and other 

 cannels, designated by Renault as Pila scotlca. It is apparently 

 beyond question from the few illustrations of this species which it has 

 been thought necessary to introduce that in the case of Pila scotica as 

 in that of the American species P. kentuckyana we have to do with 

 spores of vascular cryptogams and not with anything approaching in 

 the remotest way colonial gelatinous Algae. By the methods used in 

 connection with the present investigation it has been found possible to 

 secure large numbers of extremely thin section, which in case of doubt 

 may be made serial. The large number of sections has made it feasible 

 to choose those in which the supposed Algae are in the condition of 

 tetrads, and thus reveal their nature as spores of vascular plants. Had 

 the technique adopted here been available to Renault, there seems to 

 be little doubt that he would have escaped the error of attributing 

 the structures, which he designated Pila scotica, to algal affinities. 



Among the various appearances present by the sections of Armadale 

 coal are certain much larger spores, likewise not infrequently found in 

 tetrads, and manifesting the same alveolar structure in certain planes 

 of section through the spore wall as the species described above. 

 These appear to be what Renualt described as Thijlax britannicus.^ 

 It has not been thought necessary to illustrate these structures, as 

 their identity as spores of vascular cryptogams is entirely beyond 

 question. 



Figure 18, Plate 3, shows a section vertical to the plane of layering 

 of another coal from the Bathgate region, but not from the Armadale 

 mine, for which the writer is indebted also to Captain Halberstadt. 

 The organisms in this coal are much more numerous and are less well 

 preserved than in the case of the so-called Pilas described above. 



Near the center of the section but a little below on the right, is 

 seen with unusual clearness one of the structures, which compose the 

 coal at present under discussion almost to the exclusion of the so- 

 called fundamental substance, which makes up the mass of the bog- 

 heads hitherto described. It can be made out that the structure in 

 question is very much flattened but that the age-long pressure and 

 chemical change have not obliterated the original central cavity. Less 

 clearly marked cavities surrounded by less well-preserved walls are 



8 Op. cit., PL 21, figs. 1 and 2. 



