192 THE CANADIAN NATURALIST. [June 



buried beneath the surface. I have also ascertained that this 

 fourth stolon is in R. occidentalis, one of the radials, and always 

 when it can be seen in situ, the one pointing outwards away from 

 the nucleus. 



Fig. 11 is a vertical section of R. Jonesii, a small species which 

 occurs in the upper part of the Lower Helderberg rocks of Gaspe. 

 The shaded bell-shaped area is the central cavity. It is dis- 

 tinctly observed in several others of the same species. It will be 

 seen that the body-wall in the vault above and on the sides of the 

 cavity is thicker than it is in the base, but the tubes are much 

 more slender. They here assume the form of the elongated con- 

 necting spicula of the true sponges. Fig. 12 is a similar section, 

 though a specimen of it. Iowensis from the Trenton limestone at 

 Ottawa. At a, the central cavity is distinctly shown, filled with 

 the grey limestone matrix, which has also found its way between 

 the tubes in the base of the fossil. The shaded portions b b are 

 replaced by a reddish magnesian spar. The under side of the 

 specimen is deeply concave, and the peripheral margin is so convex 

 as to resemble a cylinder coiled into a ring. The aperture in one 

 specimen of R. Jonesii is rounded, and resembles the umbilicus of 

 an apple. 



The figures given by different authors of foreign species show a 

 considerable range of variation in the general form, and apparently 

 also in the structure of the body-wall. The details given in this 

 paper have been made out principally by the study of numerous 

 specimens of R. occidentalism which is undoubtedly congeneric 

 with R. Neptuni, the typical form of the genus. In others, such 

 as Tetragonis sulcata and T. parvipora (Eichwald), there appears 

 to be a transition to species in which the ectorhin was a soft 

 coriaceous integument, not distinctly plated, although connected 

 with the interior by tubes or spicula. The genus Tetragonis^ 

 instead of becoming obsolete, might be retained for some of the 

 species which have a structure different from that of R. Neptuni. 



As to the zoological rank of Receptaculites there yet remains 

 much diversity of opinion. At the present time the most ably 

 supported view is that which places the genus in the Foraminifera 

 near Orbitolites. Seen in this light, the diagram at the head of 

 this paper would represent the soft and not the hard parts of the 

 animal. If this be the true interpretation, then we must suppose 

 that outside of the ectorhin there was a layer of shell, and another 

 layer covering the endorhin, or lining the great central cavity. 



