J. W. Dawson on Paleozoic Rhizocarps. 23 



matrix is a gray dense shale in which the spore-sacs appear less 

 flattened and destitute of carbonaceous matter. 



(a) Sporangites B 'raziliensis, nat. size; (a x) same, magnified. 



(6) Sp. bilobatus, nat. size. 



(c) . Detached macrospores. 



(<i) Spore-cases of Salvinia natans • (d X) the same magnified. 



The very numerous spore-sacs contained in these shales are 

 extremely variable in size and form, and may have belonged to 

 several species of plants. They resolve themselves, however, into 

 two leading types, which may be provisionally named Sporangites 

 Braziliensis and S. bilobatus ; though I would suggest for them, 

 in prospect of the discovery of their vegetative parts, the name 

 Proto salvinia. Th?y may be described as follows : — 



Sporangites {Proto salvinia) Braziliensis, s. N. (fig. 1 a), 

 Sporocarps thin, carbonaceous, having a structure of dense hex- 

 agonal cells and enclosing macrospores which vary in number 

 from three or four to as many as twenty-five; form circular, 

 oval or reniform. Longest diameter from three millimetres to six 

 millimetres. Some of the sacs which do not show included round 

 bodies may have held microspores. 



S. (P.) bilobatus, s. N. (fig. 1 b) Sporocarps oval or reniform, 

 three millimetres to six millimetres in diameter, each showing two 

 rounded prominences at the ends, with a depression in the 

 middle, and sometimes a raised neck or isthmus at one side con- 

 necting the prominences. Some of the specimens indicate that 

 each prominence or tubercle contained several macrospores. At 

 first sight it would be easy to mistake these bodies for valves of 

 Beyrichia. 



The geological relations of the beds containing these interesting 

 remains are thus stated by Mr. Derby : * 



* Proceedings of the American Philosophical Society, Feb. 21, 1879. 



