NO. 2 PRE-CAMBRIAN ALGONKIAN ALGAL FLORA III 



Observations. — The resemblance between the structure of Col- 

 lenia and Cryptozoon Hall ' is marked in hand specimens as may 

 be seen by comparing illustrations of the two forms. Both have a 

 laminated appearance in sections, the concentric lamellee varying 

 in thickness and in the width of their interspaces, but when we 

 compare the mode of growth we find that Collenia has an encrusting- 

 like growth that forms a dome-shaped body with the edges of the 

 lamellae pointing downward (pi. 13, fig. i), while Cryptocoon grows 

 in a cup-shaped form with the edges of the lamellae on the upper 

 surface (pi. 16). 



Specimens of Collenia are usually small, although they attain a 

 diameter of 12 inches (32.7 cm.) or more. 



The Collenia-Uke turbinate form that I found in the Algonkian 

 series of the Grand Canyon in 1882, and sent to Sir William Daw- 

 son in 1897, had the same manner of growth as Collenia undosa 

 except that owing to its being crowded together it grew to a greater 

 height from a narrow base (pi. 15, figs. 5, 6). 



Collenia compacta (pi. 15, fig. 7) grew in part like C. occidentale, 

 but it also developed a laminated growth that filled the interspaces 

 between the more individual club-shaped forms. 



The species now referred to Collenia from the Algonkian group 

 are: 



Collenia compacta Walcott (pi. 15, fig. 7) 



Collenia ? frequcns (Walcott)* (pi. 10, fig. 3) 



Collenia occidentale (Dawson) (pi. 15, figs. 1-6) i 



Collenia undosa Walcott (pi. 13, figs, i, 2; pi. 14, figs, i, 2) 



Collenia ? sp. undt. 



Dr. J. G. Bornemann described under the name Zonatrichites an 

 algal form from the Mesozoic rocks as follows : ' 



A calcareous alga, with radially arranged filaments, forming hemispherical 

 or kidney-shaped layers, growing on or enclosing other bodies. Parallel or 

 concentric zones are seen in cross-section, formed by the periodic growth of 

 the alga, the older and dead layers serving as a foundation on which the 

 young filaments grow in radially arranged groups. 



Mr. A. C. Seward comments upon the form as follows : * 

 The nodules which are apparently formed by species of this genus occur 

 in various sizes and shapes ; Bornemann describes one hemispherical mass 8 



^ Thirty-second Ann. Rept., New York State Mus., Nat. Hist., 1883, Descrip- 

 tion of pi. 6. 



^ Bull. Geol. Soc. America, Vol. 17, 1906, pi. 11. 



' Geologische Algenstudien, Jahrb. k. preuss. geol. Landesanst. Berkakad., 

 1886, p. 126, pis. 5 and 6. 



■* Fossil Plant, Cambridge Press, Vol. i, 1898, pp. 129, 130. 



