138 



LOWER PENINSULA. 



ters. The ascending calyx walls are sometimes only slightly blis- 

 tered, and folded into stout radial rug^. In other specimens the 

 rugse are obsolete and the blisters principally obvious. A great 

 many variations in mode of growth, in the relative size of the 

 vesicles, and in distinctness of plications, can be observed among 

 the numerous specimens found in the Helderberg group and in 

 the Hamilton strata, which, upon closer investigation, may require 

 to be separated into different species, but for the present I have 

 not discovered any well-established characters upon which such a 

 division could be based. 



It occurs nearly in every stratum of the upper Helderberg group 

 and of the Hamilton group in Michigan, Canada, New York, and 

 in the Western States. 



Plate L., Upper row. — The outer left-hand specimen is from the 

 Hamilton group near Broadwell's mills, on Thunder Bay River ; 

 the two other specimens are from the Hamilton group of Widder, 

 C. W. The right-hand figure in the lower row represents silicified 

 specimens from the corniferous limestone found in the drift. 



CYSTIPHYLLUM AGGREGATUM, Billings. 



Conico-cylindrical polyparia, closely aggregated, and attached 

 to each other by the wrinkles of their surface, multiplying by 

 calycinal gemmation. Diameter of stems from two to three centi- 

 meters. Structure conformable with Cystiphyllum ; vesicles coarse ; 

 end cups moderately excavated, blistered, with faint, spinulose, 

 radiating striae. Epithecal walls likewise faintly ribbed by septal 

 rugae. Found in large clusters in the Hamilton group of Thunder 

 Bay. Not figured. 



CYSTIPHYLLUM SULCATUM, Billings. 



•Symmetrically curved, conical polyparia with a pointed apex. 

 Surface gently annulated by obtuse wrinkles of growth. Calyces 

 spacious, oblique to the axis, with erect acute margins. The sur- 

 face of the calyces generally forms a continuous laminar bag with- 

 out a blistered surface ; the marginal part of the cups is radiated 

 by rounded ruga.% broadest near the edges of the cups, narrowing 



