PALEONTOLOGIC CONTRIBUTIONS 9 



• 



terminal knobs of the calyxes, thus providing a safely hinged cover- 

 ing for the corallites. 



Hand in hand with the tightening of the covers in the gerontic 

 stage of the corallites goes the thickening of the walls and the 

 development of tabulae. While, therefore, in sections the lower, 

 older corallites are all filled with calcite, partly primary wall thick- 

 ening and partly secondary filling of the remaining cavities, the 

 habitation chambers of the upper corallites are filled with brown 

 calcareous mud. 



In looking into the shallow calyxlike depressions, in view of the 

 deep chambers of the younger portion of the corrallum, one is 

 inclined to consider these only as the casts of the opercula upon 

 the secondary filling of the chambers. This assumption is dis- 

 proved by the presence of calyxes with small, still perforated, 

 opercula (see fig. 7) in the upper, younger zones of the' corallum, 

 and further by the central cavity extending downward from the 

 calyx. 



It would thus seem that when the corallum was in the vigorous 

 growing stage the corallites had rather deep open chambers now 

 filled with brown mud ; that later these lumina became partly parti- 

 tioned off by tabulae and partly hlled by calcite, leaving only the 

 small, upper space which finally was sealed with the death of the 

 polyp by the closely fitting operculum. 



These different conditions of the corallites explain also the fact 

 that in most specimens ofF. turbinatus the top, which was 

 not covered by opercula, is either weathered away, 

 leaving a depression, as described by Rominger, 

 or is so closely attached to the matrix that it can 

 not be separated from it, as in the specimen here 

 described. 



In this connection, we have before us also a 



specimen of Ischadites squamifer Hall 



which not only exhibits on the side that was pro- 



. Ki 0- 1 Ischad- 



tected by the matrix, the surface with the rectan- ■ , ' 



J ' ltessquam- 



gular imbricating plates, such as were figured by i f e r Hall. Por- 



Conrad (Annual Report of Geological Survey, tion of interior 



1841) and Hall (Palaeontology of New York, structure. x5- 



v. 6, pi. 24, figs. I and 2, 1887), but also shows on Devonian (New 

 . , ,.,,'. . Scotland beds), 



the weathered side the interior structure as repro- ri ar ^ sv iu e -m- v 



duced in text figure 1. This agrees very well 



with that observed by Rauff (Abhandlungen k. bayer. Akademie, 



II CI. Bd. 17, 1892, pi. 7, fig. 1 ) of Ischadites murchisoni 



