276 Eepoet of the State Geologist. 



straight and continuous. Furthermore, these forms under dis- 

 cussion are of a comparatively large size, whereas the specimen 

 of the monticulatus type is a small one, representing only the 

 circumpolar region, where the reticulations, as they become 

 finer, are less distinctly indicated. The radial tubes appear only 

 as hemispherical depressions, one in the center of each rhomb. 

 ISTo details of structure are well defined. Fractures on several 

 specimens show traces of the extension of the tubes upward, and 

 one preserves indications of a roofing wall. That it is not the 

 inner wall of the basal portion to which it is at present adjacent 

 is shown by the fact, that not only does the upward prolongation 

 of the tubes fall short of the line that indicates the structure in 

 question, but furthermore it is continuous with the outer wall. 

 It is difficult, if not impossible, to determine the exact nature of 

 preservation of these specimens. The fact that they are more or 

 less silicified suggests that they represent the organism itself. 

 On the other hand, since the portion preserved exists only as a 

 surface, apparently without thickness, it seems credible that they 

 are nothing more than casts. Yet this again is contradicted by 

 the detail of the outer surface, which, on the whole, is the same 

 as that of the pyritized specimen. Perhaps the forms in question 

 result from a maceration of the original organism, producing a 

 fossil which presents both internal and external characters at the 

 same .time. 



These specimens have all been more or less preserved by silica. 

 The group described below comes from the softer portions of 

 the Shaly limestone, and is represented chiefly by casts. Many 

 exist only as reticulate, ferruginous markings on a flat shaly sur- 

 face, wKile others have, in addition, rows of rounded elevations, 

 which represent the tubes of better preserved examples. Several 

 have a circular rim which is detachable. As far as can be ascer- 

 tained from the material at hand, this rim uniformly contains on 

 both surfaces the same characteristics as the silicified specimens, 

 but in a state of poor preservation. The Lower Helderberg 

 specimens, all of which, I believe, had a subspherical or conical 

 shape when mature and whole, are now flattened so that the 

 upper portion is nearly or quite contiguous to the base. Evidence 

 relating to this point is scarce, yet it is thought that the truth of 

 these statements can be established. The loose rim, then, is the 



