346 W. H. Tivenliofel — P re-Cambrian and 



great as 10 feet across. Small secondary domes are 

 superimposed upon the larger ones. Most of the domes 

 are from 6 inches to 2 feet in diameter. The relief aris- 

 ing from these elevations appears to have been about a 

 foot. 



Each dome seems to have represented a more or less 

 separate colony which was separated from neighboring 

 elevations by V-shaped depressions in the apices of which 

 small quantities of silt collected and as the reef grew 

 upward both the separating hollows and the domes 

 appear to have held about the same relative positions. 

 As a consequence, each dome continues downward into 

 the reef as a cylindrical structure which in some cases 

 terminates at the base in a round-apexed cone. Some of 

 these cylindrical structures attained lengths of 7 to 10 

 feet. 



The structure of the reef material is laminated, growth 

 having taken place through the deposition of laminae over 

 the external surface of the dome-shaped masses. The 

 structure and general features of the ccenoplases appear 

 to be similar to those occurring in the genus CoUenia 

 Walcott of which genus this is considered a new species. 



CoUenia kona new species. 



Growths of large size ; dome-shaped on the upper sur- 

 face ; diameters varying, but mostly 2 feet or less ; struc- 

 ture consisting of superimposed laminae parallel to the 

 upper surface and hence convex upward. The laminae 

 vary in thickness from one to several millimeters, They 

 are wrinkled and in cross section appear as small anti- 

 clines and synclines of 3 to 5 millimeters amplitude. A 

 part of this wrinkling may have arisen from the pres- 

 sures to which the rock has been subjected, but probably 

 very little of it did so arise. A colony probably began 

 as an incrustation over some other substance ; but after 

 covering the bottom, more rapid growth in one place 

 than in another gave rise to domal shapes which by 

 growth upward in the same position led to cylindrical 

 structures. The upper surface of the algal reef appears 

 to have had a somewhat large-featured botryoidal aspect. 



Horizon and locality. Kona dolomite, Lower Huro- 

 nian, near Marquette, Michigan. 



The holotype and paratype are in the collections of the 

 Department of Geology, University of Wisconsin. 



