PLATE XV. 



Fig. i. Fragment of Dekayia attrita, Nich., from the Cincinnati Group of Ohio, 

 of the natural size. 



Fig. i a. Portion of the surface of the same, enlarged. 



Fig. i b. Tangential section of the same, enlarged twenty times, showing the 

 spiniform corallites scattered among the ordinary tubes. 



Fig. i c. Vertical section of the same, enlarged twenty times, showing the 

 characters of the two sets of corallites just before they open on the 

 surface. 



Fig. 2. A small specimen of Fistulipora (Callopora) proporoides, Nich., from 

 the Hamilton Group of Cariandaigua, State of New York, of the natural 

 size. 



Fig. 2 a. Part of the surface of the same, enlarged. The large circular tubes 

 have projecting and open calices, but the mouths of the interstitial angular 

 tubes are mostly closed by a calcareous membrane, and the lines of divi- 

 sion between them are only faintly indicated. 



Fig. 3. Part of the surface of Fistulipora (Callopora) incrassata, Nich., from the 

 Hamilton Group of Arkona, Ontario, enlarged. The mouths of the in- 

 terstitial corallites are seen in the specimen figured ; but they are often 

 concealed from view by a calcareous membrane. 



Fig. 3 a. Part of a tangential section of the same, enlarged twenty times, 

 showing the oval corallites with a slight constriction on one side, sur- 

 rounded by a series of angular corallites. 



Fig. 3 b. Part of a vertical section of the same, enlarged twenty times, showing 

 the remotely-tabulate oval tubes, and the vesicular tabulae of the angular 

 corallites. 



Fig. 4. Part of a tangential section of Labechia conferta, E. and H., from the 

 Wenlock Limestone of Benthall Edge, enlarged ten times, showing the 

 primitively tubular condition of the pillars, and the transversely-divided 

 edges of some of the vesicular tabulae. 



Fig. 4 a. Part of the upper surface of another specimen of the same, from the 

 same locality, enlarged. The surface-tubercles in the specimen figured 

 are more extensively confluent than is usually the case. 



