112 LOWER PENINSULA. 



a narrow circle intermediate between the central and the peripheral 

 areas, but are interrupted in their continuity outside or inside of it. 

 Inside, on the diaphragms, the plications fade away as superficial, 

 low carinations ; in the outer peripheral area their continuity is in- 

 terrupted for other reasons ; the margins of the incased plicated 

 cell cups dissolve connection and begin to diverge ; gradually widen- 

 ing gaps open between the laminar cup margins, which at first 

 continue to repose on each other's crests, but finally also these 

 become disjunct, and they remain so until at the periphera 

 surface the edges of the cup membranes join again into a com- 

 mon epithecal wall, which closes off from the outside the cavern- 

 ous gaps between them. Some of the forms have a well-developed 

 septal fovea ; in others it is not very distinct. 



BLOTHROPHYLLUM DECORTICATUM, Billings. 



Large polyp stems, conical at the base, cylindrical and flexuose 

 above, attaining a diameter of over two inches and a length exceed- 

 ing one foot. Surface, if perfect, covered by a continuous epithecal 

 crust, longitudinally striate by septal furrows and annulated by 

 deep wrinkles and constrictions. The conical basal part is deco- 

 rated with strong nodular spinulosities, as the polyp cells of the 

 associated Clisiophyllum, with which it stands in structural rela- 

 tionship. Calyces moderately deep, with steep sides, explanate 

 margins, and broad bottoms, in the form of irregularly concave 

 diaphragms, smooth in the centre, and on one side depressed into 

 a deep septal fovea. The lamelhc are acute, very prominent 

 linear crests on the ascending side walls of the calyces, but become 

 lower and almost obsolete near the expanded peripheral margins ; 

 in the broad marginal interstices between them smaller plications 

 are regularly intercalated. 



The peripheral part of the polyparia formed by the expanded 

 laminar cup margins, with large gaps between them, and supported 

 only by their ends, united in an epithecal cuticle, is very fragile 

 and rarely found in good preservation. The plurality of speci- 

 mens have lost their epitheca, and the laminar margins stand out 

 free, surrounding the stems like broad collars ; or they have been 

 destroyed, and only the central cores arc found, presenting an ex- 



