60 M. HEINRICH 



longer quite so sharp, since in many forms it is not certain whether 

 they have a greater or less degree of regularity and so are to be 

 referred to this or that genus. The differentiation into species 

 is at best dependent upon the number of lamellae and pillars per 

 millimeter, while the development of the astrorhizae and the tuber- 

 cles, on account of their variability, comes into consideration only 

 secondarily, and in extreme cases can only lead to the making of 

 varieties. 



It is especially to be noted in the work of Parks, who has recently 

 published various studies on American stromatoporids, that often 

 in one and the same specimen the conditions, e.g., the number of 

 pillars and lamellae, vary so much that one cannot be too cautious 

 in the making of new species, if the specimens are to be identified. 



In accordance with the principles above stated, the following 

 classification may be formulated: 



A. Family Actinostromldae Nicholson. Fibers massive. 



Radial and tangential elements equally well developed and united into a 

 linear network (rectilinear). (Surface therefore granular.) 

 I. Pillars passing continuously through several lamellae: Genus Actin- 



ostroma Nicholson. 

 II. Pillars only one lamella high : 



i. Lamellae quite flat: Genus Clathrodictyon Nicholson. 



2. Lamellae strongly vaulted: Subgenus Stylodictyon Nicholson and 



Murie. 



B. Family Stromatoporedae Nicholson. Fibers not massive (porous or 

 perforate) . 



I. Radial and tangential elements equally strongly developed and plainly 

 differentiated. Tangential section, however, in part vermiculate. 

 (Surface therefore in great part granular, but in places vermiculate.) 

 i. Pillars passing through: PGenus Hermatostroma Nicholson. 

 2. Pillars generally only one lamella high: Genus Stromatoporella 

 Nicholson. 

 II. Radial elements somewhat rectilinear and strongly prominent as 

 compared with the much thinner tangentials. Tangential section 

 vermiculate. (Surface vermiculate.) Genus Parallelopora Bar- 

 gatzky. 

 III. Radial and tangential elements equally strongly, very irregularly 

 interlaced (vermiculate) and therefore no longer differentiated. 

 Tangential and radial sections vermiculate. (Surface vermiculate.) 

 Genus Stromatopora Goldfuss. 



