282 Eepoet of the State Geologist. 



especially true in regard to Keceptaculites, an organism whose 

 original nature and composition are not positively known. 

 Whether composed of calcite, aragonite or chitine, it is certain 

 that it was not as enduring as most animal remains preserved in 

 the fossil state. 



Had the examination of type specimens been possible, many of 

 the ^present difficulties and contradictions which a comparison 

 with figures alone has entailed, might not have been met, and 

 those still unsolved might be satisfactorily ascribed to preserva- 

 tion or specific differences. The conclusions of Hinde* regarding 

 the structure of Keceptaculites agree so nearly in every detail 

 with those of BiLLiNas,t that it has been possible to unite the 

 results of these two authors in comparing them with my own. 

 Both writers employed for study representatives of a number of 

 different species, probably in several different modes of preserva- 

 tion. Billings, moreover, seems to have considered Ischadites 

 as a synonym for Eeoeptaoulites, and studied both genera, 

 though his conclusions refer to Eeoeptaoulites alone. 



My own observations lead to the opinion that the spicular 

 ^summit plates mentioned by these writers are an infiltration of 

 ihe rhombic pits of the outer surface or of their casts. The fact 

 that the summit-plates are admitted to be structureless and of a 

 single layer, enhances the probability of their originating in this 

 way. The four horizontal spicular rays are casts of the four 

 canals or stolons, which, in the Lower Helderberg specimen, run 

 from the radiating tubes into each angle of the rhombic pits. 

 The fact that these rays are said to be in contact with the summit 

 plate coincides with this view. Both Billings and Hinde men- 

 tion the curious circumstance that one ray, that which points 

 uway from the nucleus or basal pole, is sometimes not in contact 

 with the summit plate. 



In addition to the stolons which extend into the angles of each 

 pit, a conical spine projects into one angle and above the stolon, 

 penetrating that angle. There is, moreover, only one such spine, 

 and reason has been given for supposing that it pointed longi- 

 tudinally. The existence of this spine satisfactorily explains the 

 separation of one ray of the cast from the summit plate. 



* Hinde, 1884. Quart. Jour. Geol. Soc, vol. XL, p. 821. 



+ Billings, 1861-65. Geology of Canada. Palaeozoic Fossils, vol. I, p. 378 et seq. 



