C E. Beecher — Symmetrical Cell Development in Favositidm. 219 



quent increase, they touch and truncate each other, changing from 

 triangular to five- and six-sided prisms. Complete symmetrical 

 normal development produces a corallum with equal hexagonal 

 calices. The process of intermural gemmation changes the sides 

 of the parent cells to angles, and the older corallites, originally in 

 juxtaposition, become separated from each other by new series of 

 interstitial calices. 



Yale Museum, New Haven, Conn., May 20th, 1891. 



EXPLANATION OF PLATES. 

 Plate XIV. 



Michelinia convexa. 

 Pig. 1. Diagrammatic representation of upper surface of corallum; consisting of 



parent cell. A, and six peripheral corallites, 1, 2, 3, etc. 

 Fig. 2. The same; showing the introduction of three triangular intermural buds, 



1', 2', 3', etc. 

 Fig. 3. Third condition; with six triangular buds about the parent corallite, and 



three on the periphery of the corallum. 

 Fig. 4. Top of corallum ; showing further growth of preceding corallites, with the 



addition of three peripheral calices, 4", 5", 6". 

 Fig. 5. The same during a succeeding stage ; showing increase in size of corallites, 



and modifications produced. 

 Fig. 6. Completed growth of first system of intermural gemmation ; showing disso- 

 ciation of original series of corallites (A, 1, 2, 3, etc.), and representing condition 



preparatory for new series of interstitial corallites. 



All figures natural size. 



Plate XV. 



Michelinia convexa. 

 Fig. 7. Development of a group of corallites from initial conical cell to corallum 

 with nineteen calices. The figure represents parallel horizontal sections through 

 the corallum ; showing the number and form of the calices, their order of devel- 

 opment, and the modifications taking place during growth. The parent cell is 

 marked A ; first series of calices, 1, 2, 3, etc.; first series of intermural buds, 

 1', 2', 3', etc.; peripheral series, 1", 2", 3", etc. Notation corresponds with that 

 of preceding plate. 

 Natural size. 



Trans. Conn. Acad., Vol. VIIL 30 Oct., 1891. 



