102 LOWER PENINSULA. 



CYATHOPHYLLUM CORNICULA. 

 ZaphrenTis CORNICULA, Milne-Edwards. 



Single, conical, symmetrically curved polyparia, annulated by 

 fine wrinkles of growth, and by distant, shallow, rounded constric- 

 tions ; delicately striate in longitudinal direction by septal furrows ; 

 apex pointed ; calyx deep, with suberect margins gently spreading 

 near the edges. Bottom of calyces variable ; there are specimens 

 in which the calyx gradually narrows into an obtuse pit ; in others 

 the bottom is reflected into a moderately convex protrusion, on 

 which the lamellar crests unite ; or this protrusion of the reflected 

 bottom is of annular form, with a depression in the centre, which is 

 confluent with a well-developed septal fovea situated on the convex 

 side of the curvature of the horn-shaped polyp cells. The lamellae 

 are alternately large and small, denticulated on the edges and 

 carinated on the side faces ; from sixteen to eighteen carinae on the 

 space of one centimeter's length. Number of lamellae in calyces 

 of two centimeters diameter, from seventy to eighty. Lamellar 

 interstices of the peripheral area filled with vesiculose, transverse 

 plates up to the margins of the end cups, but the edges of the 

 lamellae remain free to some extent, more so than in the former 

 species. The central area is intersected by well-developed trans- 

 verse diaphragms, of somewhat irregular compound structure, join- 

 ing the outer vesiculose area with depressed margins. The largest 

 sized specimens are about six centimeters long, by a diameter of four 

 centimeters at the calycinal margins ; but the majority of specimens 

 are much smaller. It occurs in the upper Helderberg strata of 

 Michigan, Ohio, Canada, New York, and in the Western States, as 

 one of the most abundant and characteristic fossils of that horizon. 



Plate XXXV., Lower tier. — The left-hand group of specimens 

 represents different variations of the kind found in the drift of Ann 

 Arbor, all in silicified condition, with exception of the upper 

 largest specimen, which is calcified ; the other specimens are from 

 the Falls of the Ohio, and from Columbus, Ohio. 



