PAL^ONTOLOG Y.] I 2 9 



Phillipsastrasa VerneuilH, but the two forms arc not found associated 

 on Mackinac Island. It is doubtful to me whether Owen's species 

 is identical with this form ; the figures and descriptions given by 

 him are insufficient to determine the question positively. Another 

 large form of Phillipsastrsea, for which I propose the name of 

 PJiillipsastrcca Yandclli, is found in the Helderberg limestones of the 

 Falls of the Ohio, and in silicified condition, often loose, in the drift 

 of that vicinity. It differs from the described form in having 

 much more spacious central cell pits, not surrounded by a raised 

 rim. The bottom of the cells is formed by a large convex pro- 

 tuberance on which the lamellae unite ; diameter of cells from three 

 to four centimeters ; inner cell pit one and a half to two millimeters 

 wide ; exterior outlines of calyces obscurely defined. Not repre- 

 sented for want of space. 



. STROMBODES, Schweigger. 



Compound polyparia, formed of radiated polyp cells united, with- 

 out defining walls. The cells are either confluent, without any 

 peripheral demarkation, or they join under obtusely crested poly- 

 gonal outlines, which inclose shallow calycinal depressions with an 

 abrupt central pit. The surface impressed with these pits forms a 

 continuous laminar expansion, and the growth of the polyparia 

 consists in a constantly repeated production of such laminae ; where- 

 fore we find them formed of a superimposed series of such layers. 

 The walls of the abrupt central depressions of the 'calyces, which 

 correspond in the layers, combine by invagination into cylindrical 

 central cores, extending, without interruption, through the whole 

 length of the corallum ; the crest-like plications in the circum- 

 ference of the inner cell pits form a cycle of vertical lamellae, which 

 intersect this central core. The horizontally spreading marginal 

 portions of the superimposed calyces are not in immediate con- 

 tiguity ; between each layer an interstice exists, which is filled 

 with unequally interlaced, blister-like vesicles. This indicates a 

 periodicity in the growth of the polyparia by which at one time 

 fully finished, radially plicated, continuous laminar calyces were 

 formed, and in time for the abandonment of the old cells and prc- 



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