Lower Helderbekg Fauna. 2Y3 



perplexing organism. In section, this specimen, described in 

 detail below, has the outline represented by the diagram on 

 Plate. Ill, figure 1. The edges are ragged, indicating that it is not 

 complete, and probably preserves only the basal portion of a form 

 which, when perfect, had somewhat the proportion of a pine cone 

 (as described by Eauff). The surface structure consists of ridges 

 which start from a point, the basal pole (Rauff), and radiate 

 spirally in two directions, after the manner of the engine-rolling 

 on a watch. The ridges are thin, solid, high, and usually con- 

 tinuous. The rhombic depressions which they form are well 

 marked and deep. This description is true of both surfaces, but 

 that one which is here called the gastral surface has the reticula- 

 tion much reduced, perhaps one-fourth the size of the other. A 

 comparison of the two surfaces may be made by referring to 

 Plate II, figure -i, and Plate III, figure 1. Both faces are retained 

 in an equal state of preservation, an unprecedented occurrence 

 with the Lower Helderberg Receptaculhes, the interior of which 

 is rarely preserved at all. 



In this incomplete example, the basal pole exists only on the 

 gastral surface, where it is partly covered over. It may be 

 inferred with certainty from other specimens, that a siniilar pole 

 existed on the outer basal surface, directly beneath the gastral 

 one. In general terms the organism consists of a a outer and an 

 inner, or gastral wall, connected by perpendicular processes. 

 Each of these walls has, of course, an outer and an inner surface. 



The Outer Wall. 

 Plate III, figures 2, 3, 4. 

 The radiating ridges above referred to, intersect at regular in- 

 tervals and form slender pillars at those points. From each of 

 these pillars, near its outer end, there projects toward the right 

 a peg-like spine, short, cylindrical and bluat. Across the floor 

 of each rhomboidal pit, between opposite angles run two rounded, 

 fusiform channels. These channels extend well into the corners 

 of the pit, where they make slight indentations. In the middle 

 of each pit, at the point of intersection of the channels, is a still 

 further depression. This is circular in outline or sometimes 

 diamond-shaped, contracting slightly as it descends, and, at its 

 base, communicates with a tube which serves to connect the inner 

 with the outer wall. 



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