144 



LOWER PENINSULA. 



seem to differ much from the smaller ^specimens except by a cen- 

 tral compressed cristiform projection similar to the columella of 

 Cyathaxonia, which is broken in the represented specimen, but is 

 distinctly developed in other specimens found there and at Louis- 

 ville. I hesitate ^therefore to identify the larger specimen with 

 the smaller form. The subsequently described species have all a 

 well-developed septal fovea, and are considered to represent the 

 genus Zaphrnitis proper. 



ZAPHRENTIS STOCKESII, Milne-Edwards. 



Symmetrically curved conical polyparia, sometimes elliptical in 

 outlines by a compression in a direction transverse to the curva- 

 ture. Length of cones about twice the diameter of the calyces, 

 which in middle-sized specimens is about four centimeters. Ca- 

 lyces moderately deep, wath erect margins and a spacious subcon- 

 vex bottom, on which the lamellae unite in an irregularly twisted, 

 interlacing manner as low carinae. Lamellae linear, stout ; sixty 

 to sixty-five larger ones alternating with as many small rudimentary 

 crests may be counted in the circumference of calyces four centi- 

 meters wide. A large septal fovea is situated in the median line 

 of the convex side of the curved polyparia. Transverse diaphragms 

 well developed ; the crests on the upper side do not connect into 

 continuous vertical leaves with those of the succumbent cups ; 

 the lower side of the diaphragms is generally smooth, not crested. 

 The external walls of the specimens are rarely preserved in the 

 silicified condition, and the excoriated surface is longitudinally 

 ribbed by the exposed vertical plications. In some specimens, 

 however, the superficial epithecal crust is perfectly preserved. 

 Found in the Niagara group of Drummond's Island, Point Detour, 

 and in the same formation at Masonville, Iowa. 



Plate LI., Lower row — The two largest specimens. The upper 

 one, on the left-hand side, is a side view of an excoriated specimen 

 from Point Detour. The one on the right-hand side of the plate 

 exhibits the bottom of a calyx and the position of the septal 

 fovea ; the erect marginal parts are broken off. The second figure 

 from the left, in the lower row, is also a young specimen of this 

 kind. 



