THALLOPHYTA 



CLASS ALGAE 



Genus GRYPTOZOON Hall 



CRYPTOZOON PROLIFERUM Hall * 



Plate XXVIII, Figs. 1, 2; Plate XXIX, Fig. 1 



Cryptozoon proliferum Hall, 1884, 36th Rept. New York State Mus. Nat. 



Hist., pi. vi. 

 Cryptozoon proliferum Walcott, 1912, Smithsonian Misc. Coll. 57, p. 258, 



pi. xxxvii, figs. 1-3. 



Description. " These bodies are made up of irregular, concentric 

 laminae of greater or less density and of very unequal thickness. The 

 substance between the concentric lines, in well-preserved specimens, is 

 traversed by numerous, minute, irregular canaliculi which branch and 

 anastomose without regularity. The central portions of the masses are 

 usually filled with crystalline, granular, and oolitic material and many 

 specimens show the intrusion of these extraneous and inorganic sub- 

 stances between the concentric laminae. That these are intrusions, and 

 not inclusions, is shown from the fact that they can be traced to a vertical 

 fissure or break leading to the exterior of the fossil and which allowed the 

 crystalline matter to enter." Hall, 1884. 



As noted under the following species, Cryptozoon proliferum is char- 

 acterized by its growth from a widely expanded, almost flat, series of 

 lamellae into confluent heads of a size varying from four or more inches 

 in diameter at the center of a growth to small, concentric areas an inch or 

 less wide on the edge. 



* In the specific bibliography throughout this volume only the original and 

 the more important subsequent references are cited. The complete bibli- 

 ography for the Post-Cambrian forms may be consulted in the Bibliographic 

 Index of American Ordovician and Silurian fossils published as Bulletin 92, 

 U. S. National Museum. 



