238 



PROF. H. A. NICHOLSOJf AT?D DE. J. MUEIE ON THE 



bling interlaminar spaces, and, moreover, the fossilized calca- 

 reous nature of tlie whole — undoubtedly simulated in a forcible 

 manner the characters of Stromatopora in vertical section. This 

 will readily be allowed if fig. 13, PL lY., be compared with fig. 3, 

 PI. I. If, again, the surface of one of the layers of Eschara 

 nobilis, fig. 12, PI. lY., be compared with the surface of the 

 concentric laminae of Btromatoj^ora tuberculata, fig. 2, PI. I., less 

 likeness is discernible, though the weathered protruding pillars 

 and pseudo-orifices of the latter may at first sight be taken for 

 the cell-orifices of the former. 



Closer inspection, however, does not bear out such apparent 

 agreement ; for the regularity in shape and position of the cells and 

 orifices of the j^olyzoarium of this species of Eschar a {Hemescliara, 

 Busk), avicularia, and other secondary features are completely at 

 variance with the structural surface-peculiarities of S. tuberculata 

 and all other species of the genus. But even the general similarity 

 of facies of vertical sections between the two forms in question 

 diminishes in proportion as detailed and microscopic investiga- 

 tion is pursued ; and from such Stromatoporoid genera as Cauno- 

 pora, Sfylodictyon, &c., the polyzoarium of Eschara departs still 

 further. Another genus of the family of Escharidge, namely 

 Betepora, occasionally, to a certain extent, simulates the minute 

 vesicular structure of Clathrodictyon ; but the general fenestrated 

 foliaceous nature of its polyzoarium, presence of avicularia, mar- 

 ginal spines, ovicells, &c., sufiiciently distinguish Polyzooid from 

 Stromatoporoid organization. Among the family of Celleporidae 

 again, in certain of its forms, sufficient likeness can be traced 

 to justify a comparison with Clathrodictyon, and partially, it may 

 be, with Stylodictyon. Here, in the genus Cellepora, the erect di- 

 cliotomously branched species must be excluded, and only the 

 globose spreading adnate forms taken into account. Even these 

 latter seldom, if ever, assume the outward form of the Stromato- 

 poroids, not excepting the recent Cellepora mammillata, with its 

 incrusting polyzoarium and surface-projections. Their vertical 

 or horizontal section in mass, though, does assume something of 

 the cellulo-vesicular character of similar sections of Clathro- 

 dictyon. The heaping together and vertical inclination of the 

 cells of the polyzoarium of Cellepora is, however, only a decej)tive 

 likeness • for even in the fossil species of the genus the punc- 

 tured or sculptured character of the cell-walls, the presence of 

 rostra, avicularia, ovicells, and often denticles, sinuses, or spines, 



