292 Eeport of the State Gteologist. 



On the other hand, Syringosteoma seems well able to stand as 

 a genus without, the support of Actinostroma Bistigouchense^ if 

 the characters attributed to it by JSTicholson from a study of 

 S. densum hold good. 



The Lower Helderberg representatives of this genus, if cor- 

 rectly ascribed to Syeinoostroma, agree in many respects with 

 S. densum. As far as examined, they are all normal and exhibit 

 well-marked Stromatoporoid characters. The division of the 

 coenosteum into latilaminse is usually conspicuous, as are also the 

 large astrorhizae often situated on monticules with a tubular axis. 

 Tangential sections of well-preserved specimens show a doubly 

 porous structure. In the first place, the skeleton is rendered 

 pumicious by the presence of numerous vacuolse, usually of an 

 elongated or vermicular form. This appearance resembles that 

 common in Stromatopora, and is easily seen when slightly magni- 

 fied or even with the naked eye. Further, the skeletal tissue 

 itself is of a minutely porous character, and appears to be com- 

 posed of a mesh of anastomosing fibers. This structure suggests 

 the system of radial pillars joined by horizontal arms character- 

 istic of Actinostroma, but such interpretation is discountenanced 

 by a study of vertical sections. Viewed in radial section, the 

 skeleton is seen to be composed of laminae and radial pillars, 

 which are continuous and usually of large size. Instead of being 

 dense and granular, as in Actinostroma, these have the same mi- 

 nutely porous structure as the laminae. Moreover, although the 

 pillars are usually superimposed and continuous in that sense, 

 they are not the controlling structural element as in AoriNos- 

 troma. It often happens that the dark lines which demarkate 

 different lamiiiee pass continuously through the pillars, cutting 

 them into many sections or drums. Each of these is continuous 

 with the lower portion of the lamina immediately beneath it, and 

 is terminated by the upper face of the lamina above. 



Thus, while Syringosteoma unites structures characteristic of 

 both Actinostroma and Stromatopora, and in an intermediate 

 form between the Hydractinioid and Milleporoid groups of 

 Stromatoporas, in typical examples, its separation from any other 

 genus is attended with little difficulty, and its validity as a 

 separate type seems certain. It resembles Stromatopora in the 

 poro-fibrose structure of the lamina, but is without the tabulate 

 zooidal tubes of that genus. I^either by implication nor by direct 



