146 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



DESCRIPTION OF PLATE 18 



PAGE 



Greysonia basaltica Walcott. ( See pi. 17) 109 



Fig. I. (Natural size.) Vertical section of a group of tubes forming 

 a layer 5 cm. in thickness. U. S. National Museum, Cata- 

 logue No. 60715. 

 The tubes are filled with a bluish-black limestone and the algse 

 are represented by gray to grayish-yellow magnesian limestone. 



The tubes were formed, in a horizontal position, presumably as 

 portions of a large frond. 

 2. (Natural size.) Lower surface of a specimen of which the 

 upper surface is represented by fig. 2, pi. 17. U. S. National 

 Museum, Catalogue No. 60714. 

 The tubes of this specimen appear to have grown in a vertical 

 position, and have a length in the portions preserved of 18 cm. 



The specimens represented by figs, i and 2 are from locality 400c: 

 Algonkian : Newland limestone; 8 miles (12.8 km.) west of White 

 Sulphur Springs, Meagher County, Montana. 



