PLATE V. 



FaVOSITES HEMISPHERICA V;ir. DISTORTA. 



Fig. I. A large individual of this species, which has assumed a zigza.a: direction in its progressive 

 stages of growth. 



Fig. 2. Another individual which has made a complete turn in an irregularly spiral direction. 



Fig. 3. A smaller specimen which has turned nearly at right angles in its progress of growth. 



Fig. 4. A smaller specimen which, in its progress of growth, has become turned almost birectangn- 

 larly, the direction of the last stage of growth being precisely opposite to that of 

 its commencement. 



Fg. 5. A few of the cell-faces enlarged, showing the concentric growtli of the operculiform epi- 

 theca. From the Limestone of the Upper Helderberg group in the Helderbei'g 

 Mountains and at Schoharie. 



This variety, and the cyathophylloid forms of the species were erroneously identi- 

 fied by Eaton with Cyathophyllura quadrigemiiium. of Q-oldfuss, from the radiation of 

 the cells as they commonly appear upon the weathered surfaces. 



