Lower Heldekberg Fauna. 27 Y 



lateral portion of the organism, which, being even at first the 

 thickest part of the wall, and now double, proved less destructible 

 than the base and the fragile top. 



Obsekvations on Other Lower Helderbebo Specimens, f?^ 



The form of Receptaculiies infiondibuliformis is " usually- 

 discoid, sometimes broadly infundibuliform. The upper surface 

 is more or less depressed with frequently a small conical projec- 

 tion in the center."* Whether the specimens are regarded as 

 entire individuals of an original saucer shape, or, as Rauff 

 claims, are merely basal portions of a cone-shaped test, the 

 orientation of the fossil is attended with few difficulties on 

 account of the curvature of the surface and the starting point of 

 the radiating-ridges. The surface uniformly preserved, which is 

 convex in the better specimens, is either the outer or inner sur- 

 face of the outer wall. That this surface is not the inner wall, 

 is shown by the curvature and by tubes which are seen in 

 traces directed upward from the concave side. Furthermore this 

 circumstance is the natural result of the physical conditions 

 which attend the burial of such an organism. The base would be 

 more or less protected and preserved by the bottom on which it 

 rested, while the upper part, and later, the gastral wall of the 

 lower, would lie exposed to the destructive and solvent action of 

 the sea until covered over by the gradual deposition of sediment. 

 As has been said, which surface of the outer wall is represented 

 can not be determined in all cases. 



In the case of the pyritized specimen the curvature of the sur- 

 faces is misleading. It suggests that the inner wall is in fact the 

 outer, and that the outer or concave side bounds the gastral 

 cavity. However, the structure of the coarsely reticulate surface 

 corresponds in a general way to that of specimens from other 

 horizons whose orientation is known, showing that it is the outer 

 wall. The reticulations agree in size and character with those of 

 the common Lower Helderberg forms. This fact warrants the 

 identiScation of this fossil with B. infundihul'iformis, and at the 

 same time confirms the orientation of surfaces here adopted. 



* Hall. 1887. Pal. New York, vol. VI, p. 290. 



