66 LOWER PENINSULA, 



placed by him with the Zoantharia perforata, is intimately related 

 to Thecia. It is composed of short conical tubules, communicat- 

 ing by lateral pores, radiated by twelve granuloso-spinulose 

 crests, and intersected by convex diaphragms of spinulose 

 surface. The tubules are incrusting and never attain any great 

 length. 



THECIA MAJOR, N. Sp. 

 (Compare Favosites Forbesii. Roemer, Silur. Fauna of Tennessee.) 



Discoid, lenticular expansions, covered on the lower side by a con- 

 centrically wrinkled epitheca, with diverging striae, indicating the 

 outlines of procumbent tubes, which bend into an erect position 

 before they open on the upper surface of the disks. Diameter of 

 tubes two millimeters, joining under well-marked, obtusely crested, 

 polygonal margins, which inclose dilated orificial pits. Walls 

 stout, but variable in thickness in different portions of the same 

 specimens. Twelve radial crests extend half way to the centre ; 

 their edges are decorated with two rows of granulose spinules. Di- 

 aphragms numerous, partially flat, partially convex, forming a mon- 

 ticulose projection with spinulose or granulose surface. Pores large 

 and abundant. Occurs in the Niagara group of Drummond's Island, 

 Point Detour, and in many other localities on the south shore of 

 the Upper Peninsula. Found also in abundance at Charleston 

 Landing, Indiana ; at Louisville, Ky., and in many Niagara out- 

 crops of the West. 



Plate XXV. — Fig. i, specimens in calcified condition seen from 

 the upper and lower side, both from Charleston Landing, Indiana. 

 Fig. 2 represents a silicified specimen found at Point of Barques, on 

 Lake Michigan. The upper end of the specimen exhibits well- 

 preserved tube orifices with radial crests, convex diaphragms, spinu- 

 lose surface decorations, etc. ; the lower portion is formed of tube 

 casts with flat diaphragms, crcnulated at the circumference by the 

 indentations made by the radial crests of the walls ; the perfect 

 correspondence of the structure of Thecia with Favosites is most 

 beautifully to be seen in the represented specimen. 



