,278 Kepoet of the State Geologist. 



Conclusions. 

 Specimens of R. infundibuliformis^ as ordinarily preserved, 

 are so ambiguous in character that the current views on Eeohp- 

 taculites would probably have been regarded as satisfactory 

 had not a remarkable specimen opened the way to a new 

 interpretation of the structure of this genus. 



I. The Form. 



That Receptaculites and Isohadites were siibspherical, when 

 entire, and inclosed, or nearly so, is the position taken by 

 Billings, which Radfe confirms. Hinde, however, follows 

 Saltee, and considers that Ischadites alone had this form, and 

 that Rejoeptac[jlites was a flat, platter-shaped organism, in which 

 condition it at present usually occurs. 



The evidence afforded by the Lower Helderberg Reoep- 

 taculites is not of a positive character, but, on the whole, seems 

 to support the view of Ra^uff and Billings. The regular 

 circular outlines which unbroken specimens maintain might 

 appear to indicate an explanate organism. On the other hand, 

 a homogeneous, top-shaped or spherical test, flattened by down- 

 ward pressure, would assume .the same form. This supposition 

 is further borne out by the specimen with traces of a roofing 

 wall and those with a detachable rim. If the sides were 

 extended so as to completely inclose a central cavity, the upper 

 portion must have been of extreme tenuity. 



II. structural Elements, 

 (a) The Summit Plate. — According to the generally accepted 

 construction of Receptaculites, the radiating ridges should 

 represent part of the matrix thrust in between the summit plates 

 of the spicules, the plates themselves being subsequently 

 dissolved away. The radial tube would be interpreted as the 

 perpendicular ray, and there also should be four other rays 

 forming diagonals of the rhombus. Two of the rays would 

 thus be directed lengthwise or meridionall}^, and the other two 

 at right angles to these. JS^ot only have none of these supposi- 

 tious summit plates been observed on Lower Helderberg speci- 

 mens, but there is no evidence that they ever existed. Three 

 suppositions concerning them are possible : (1) they were loose, 



