74 LOWER PENINSULA. 



broadly attached with the centre ; marginal parts free and covered by 

 an epitheca. Diaphragms nearly flat, often simple, and scarcely 

 vesiculose, closely approximated ; other times the vesiculose char- 

 acter is more pronounced. Pores small, irregularly distributed. 

 Longitudinal stri?e and spinulose rows much more delicate and 

 minute than in the other species. 



Found in the drift of Michigan, and in the corniferous lime- 

 stone of Canada and New York. 



Plate XXVII. — Fig. 4 represents a silicified specimen found in 

 the drift of Ann Arbor. 



MICHELINIA INSIGNIS, N. Sp. 



Lenticular convex disks of large size, formed of diverging tubes, 

 prostrate on the lower side, and composing by their united walls an 

 epithecal crust with diverging, radial ruga^, and with annular, con- 

 centric wrinkles of growth. Diameter of tubes from two to three 

 millimeters. Tubes sometimes moderately stout-walled and join- 

 ing with acute margins of polygonal outlines ; at other times the 

 walls are thickened, somewhat dilated at the orifices, with obtuse 

 rounded interstitial margins. In the same specimens elsewhere, 

 the orifices of the tubes may be projecting, with raised circular mar- 

 gins, and the sides of the tubes may be found only in loose lateral 

 contiguity with teretiform walls, and annulated by fine wrinkles of 

 growth, with faintly indicated longitudinal striation. The tube 

 cavity is lined by from thirty to forty longitudinal rows of spinules 

 or spinulose ridges, which project nearly to the centre of the tubes 

 as radiations. Diaphragms closely set, concave, simple or com- 

 pound, of vesiculose plates. Pores numerous, small, irregularly 

 dispersed. Found silicified in the Hamilton group near Alpena, 

 also in the Hamilton group of Darien, N. Y., in calcified condition; 

 likewise in the Helderberg group of the Falls of the Ohio, and in 

 several other localities of Kentucky, Crab Orchard, etc. 



Plate XXVII. — Fig. i is a fragment of a large mass in calcified 

 condition, found at the P'alls of the Ohio, presenting a vertical sec- 

 tion. Fig. 2 is a silicified specimen from Alpena, Thunder Bay, seen 

 from the under side. Fig. 3 is the same, seen from above. 



