96 LOWER PENINSULA. 



ing centres of which leaves, one invaginated into the other, form 

 the cristiform columella, and not the united central ends of the 

 vertical lamcllne, which do not perfectly reach the centre under the 

 form of uninterrupted vertical leaves ; their inner termination is 

 only a superficial carination on the conical centres of the dia- 

 phragms. This structure does not materially differ from the 

 structure of many genera of the Cyathophylloids, particularly of 

 some forms of Zaphrcntis and Trochophyllum. The latter genus 

 may be said to differ from Cyathaxonia only in the inverted direc- 

 tion of their invaginated diaphragms. In Trochophyllum the dia- 

 phragms form deep, funnel-shaped depressions in the centre of the 

 cells, which, in their invaginated condition, likewise compose a solid 

 central axis, turned inward instead of projecting. Cyathaxonia 

 is not found in the strata of Michigan. The specimens described 

 from the upper coal measures as Lophophyllum proliferum, Mc- 

 Chesney, is a genuine form of Cyathaxonia, entirely corresponding 

 in structure with the forms of Cyathaxonia, described by Milne- 

 Edwards, from the sub-carboniferous strata of Kentucky. Palaeon- 

 tologists examining these well-preserved specimens observed at 

 once the existence of transverse leaves across the radiated inter- 

 stices of the calyces, and hesitated on that account to identify 

 them with Cyathaxonia ; had Milne-Edwards examined his type 

 specimens somewhat more carefully, he would have noticed in 

 them the same transversal leaves. 



CYATHOPHYLLID^. 



Simple or compound polyparia formed of cell cups margined by 

 .a cycle of plications of an apparently radial position toward the 

 centre of the cells, but actually disposed according to the bilateral 

 plan peculiar to the whole order of the Zoantharia rugosa. 



The polyparia are built up by a successive series of such cups, 

 one invaginated into the other, with gradually increased size. In 

 some forms the cups are clearly defined in their superposition 

 by a more or less distinct lamination in the structure of the poly- 

 paria ; in others the union of the cups is more intimate. The pli- 

 cations of the incased, cups corresponding, and clasped over one 

 another, grow together and form continuous vertical laminae, while 



