Lower Heldeebeeg Fauna. 293 



statement does Nicholson refer this structure to jS. densum. 

 Moreover, the interzooidal spaces are regularly arranged into 

 columns, and the more minute division into laminae is conspicuous, 

 which is never the case in Stromatopora. 



While the radial structure of Syringostroma is suggestive of 

 AcTiNosTROMA, the pillars are porous, not granular. They are 

 either confluent with, or terminated by the laminae. 



In most of the Lower Helderberg specimens the laminae appear 

 in radial section of a darker color than do the radial pillars which 

 support them. In a similar way the monticules are still darker 

 than the rest of the laminae, and become prominent to the eye on 

 that account. Whether this circumstance is due to a dijfference 

 in density of the skeletal tissue, or is owing to mechanical causes 

 governing infiltration or replacement, I have been unable to 

 determine. 



The preparation of drawings to illustrate the newly described 

 material was attended with some difficulty, for it was almost 

 impossible to depict the sections as they appeared with fluctua- 

 tions of shade and distinctness, and with the gradations through 

 which the dark fibers of the skeletal tissue passed into the nearly 

 colorless calcite in filtering the vaculae or chambers. Conse- 

 quently the annexed figures partake somewhat of the nature of 

 restorations, for they are intended to convey the expression of 

 the original, without faithfully reproducing its defects or defic- 

 iencies. At the same time they do not aim to present the organ- 

 ism in the condition in which it perished and became imbedded 

 in the marine deposits. 



Syringostroma centrotum, sp. nov. 

 Plate VII, figures 1, 2. 



Coenosteum massive, spheroidal, often attaining a large size. 

 Intermittent concentric growth results in the formation of lati- 

 laminae, which are usually conspicuous. The surface is thickly 

 covered with rounded eminences or " mamelons," and astrorhizae 

 are numerous but minute. The presence or absence of an 

 epitheca has not been ascertained. 



ISTo specimens in this collection are entire, but all evidence 

 points to an originally sphaeroidal form for the coenosteum. 

 One specimen appears to have had a diameter of about 27 cm. 

 when entire. The concentric character of the structure is usually 



