I04 LOWER PENINSULA. 



edges of the lamellae within the calyces are covered with granula- 

 tions and by short, interrupted, transverse carinations or rugosities. 

 The transformation of the linear radial crests into roof-shaped plica- 

 tions on the ascending side walls of the calyces alters the structure 

 of the peripheral area considerably. There are no small, vesiculose, 

 interstitial plates developed in the interstices between the radial 

 crests, as in the outer area of other Cyathophylla ; the lamellae 

 themselves open in two diverging leaves,which join in the interstices 

 into a continuous calycinal membrane of a blistered structure. 

 The calycinal surface represents a complete laminar bag folded 

 into plications, with the acute edges of the folds directed inward, 

 and the rounded curve turned outward. The coral is formed by 

 invagination of a series of such bags, which have elongated, blister- 

 like intervals between them, but are in intimate connection by the 

 edges of their crested plications, which correspond to each other 

 and combine into vertical laminar dissepiments extending through 

 the whole length of the corallum. In the marginal portions of the 

 calyces, however, the crests are often interrupted in their vertical 

 continuity by the extension of the blister-like interstices between the 

 calycinal bags across several of the plications which have lost their 

 edged crest form through spreading into a tent-shape. This struc- 

 ture frequently causes an exfoliation of the surface of the speci- 

 mens, with exposure of the outer blistered surface of the bags, by 

 which even small fragments can be identified as belonging to this 

 species. The central area is septate by transverse diaphragmatic 

 plates of much regularity. The vertical lamellae intersect them as 

 continuous leaves nearly to the centre. Occurs as the prevailing 

 species in the Hamilton group of Thunder Bay and of Little Tra- 

 verse Bay. A coral described by Hall under the name of Chono- 

 phyllum ellipticum, from the Hamilton group of Iowa, agrees in 

 structure with the described form, but not with Chonophyllum. A 

 similarly built species is found in the upper Helderberg strata of 

 Kentucky, but both of these, according to their mode of growth, 

 seem to differ specifically from our form. 



Plate XXXVI. — In the upper row of figures are views of dif- 

 ferent specimens found at Little Traverse Bay. The central larger 

 specimen presents a polished section. 



