Lower Heldeeberg Fauna. 283 



The radial pillars are said to be continuous with the summit plates 

 and they must be preserved and represented in the same way. 

 The summit plates are regarded as casts of rhombic pits. Hence 

 the radial pillars seem only infiltrations filling the radial tubes. 

 On this basis, the spicular canals, the presence of which has 

 been confirmed by many writers, would be the result of an incom- 

 plete process of deposition. 



The character of the inner wall does not appear to be definitely 

 made out by any of the investigators who have written on 

 Receptaculites. In the case of R. infundihuliformis, my own 

 observations are not wholly satisfactory. The salient features of 

 the descriptions given by Hinde and Billings are that (1) it is 

 probably not composed of separate plates like the outer wall, 

 but many examples show a continuous layer; (2) this is pierced at 

 regular intervals by round holes arranged in a quincunx order, 

 and these perforations are sometimes connected by furrows which 

 apparently mark off the surface into rhombic plates similar to 

 those beneath, with which they are joined by the radial pillars; 

 (3) in the body of each plate lie four canals running from the 

 center (the point of union with the radial pillars) to the middle 

 of each side, where they join the canals similarly situated, of the 

 four plates adjoining. Rauff regards both perforations and 

 canals as the result of fossilization. If Rauff's conclusion is cor- 

 rect, the endorhin need not be discussed. If, on the other hand, 

 the traces interpreted by Hinde and Billings stand for real 

 structures, the distinction between the ectorhinal and endorhinal 

 canals should be noted. 



" The stolons run along the inner surface of the ectorhin, but the 

 endorhinal canals are excavated in the substance of the endorhin."* 

 Since the canals in the Lower Helderberg species run longitudin- 

 ally and the endorhinal canals spirally, it is diificult to regard the 

 two as identical. Should this, however, be the case, the distinc- 

 tion pointed out by Billings corresponds to a difference between 

 the canals of the outer and inner walls, as shown in B. infundib- 

 uliformis. In the ectorhin, the canals are trenches in the 

 bottom of rhomboidal depressions ; in a cast, they would appear 

 like stolons attached to a rhomboidal plate ; yet, in the endorhin, 

 they are enclosed as described by Billings and Hinde. 



* Billings 1861-5. Geol. of Canada, Palaeozoic Fossils, p. 382. 



