J. W. Dawson on Paleozoic Rhizocarps. 25 



of the valley, there are, on the Tapajos, shales containing Spiro- 

 phyton and calcareous concretions, which were referred pro- 

 visionally to the Carboniferous by Prof. Hartt, but which seem to 

 me to be Devonian, and I refer to the same age the black shale 

 found by S u r Penna on the XingCi." 



I have not seen specimens of the black shales referred to in 

 this description, but should think it likely that on careful exam- 

 ination they might be found to owe their carbonaceous or bitu- 

 minous matter to the partial decay of Sporangites. They also 

 deserve careful examination, with the view to the discovery of the 

 vegetation appertaining to the sporocarps. The similarity of these 

 Brazilian beds to those holding similar fossils in Ohio and Ontario 

 is very striking. 



There can be no question of the close resemblance of the 

 Brazilian species of Sporangites with the spore-envelopes of modern 

 Rhizocarps. Some individuals of the S. Braziliensis are scarcely 

 distinguishable in form or contained macrospores from the sporo- 

 carps of Salvinia natans of the rivers of Europe (fig. 1 d). It is 

 true that the analogy of Salvinia would lead us to expect other 

 sacs containing microspores ; but in ordinary circumstances the 

 latter could not be preserved in a visible state, and in the Brazi- 

 lian shales there are many specimens not showing macrospores, and 

 which might have been filled with microspores which had been 

 flattened into an undistinguishable mass. 



If we compare the separate microspores of the Brazilian sporo- 

 carps, and especially those which are found detached from their 

 envelopes, with Sporangites Haronerisis, we see a remarkable 

 similarity in size, form and texture, sufficient to justify us in 

 supposing that the latter miy be of the same nature with the 

 former, but deprived of their outer cases either by dehiscence or 

 by decay, and this is the view which I am now disposed to take of 

 their nature, and which better accords with their wide distribution 

 in aqueous deposits and with their accompaniments than any other 

 supposition. I may add that Prof. Orton and Prof. Clarke, in 

 letters to the author, refer to grouping of the little rounded bodies 

 and traces of enveloping membrane. In this connection I would 

 also mention the sacs containing rounded bodies known as Parka, 

 and which have been met with in the Erian beds both in Scotland 

 and in Gaspe, and have been supposed to be ova of crustaceans. 



