126 



PROTOZOA. 



in the Laurentian limestones of Canada, and which he states 

 to be surrounded by a tubulated calcareous shell, resembling 

 the " proper wall " of Eozoon. He is of opinion that these 

 bodies are either detached chamberlets of Eozoon, or that 

 they are independent organisms, allied to Eozoon, but of a 

 simpler type. 



EECEPTACULITES. 



Before leaving the Fomminifera, we must briefly consider 

 the curious fossils grouped together under the name of 

 Receptaculites (figs. 28 and 29), which appear to constitute 

 an aberrant type of the Foraminifera. If truly referable to 

 this group of animals, Eeceptaculites is not only highly abnor- 

 mal in point of magnitude, being sometimes as much as a foot 



in diameter, but its actual 

 structure is quite anomal- 

 ous. The genus includes 

 large fossils, which are usu- 

 ally discoid, basin-shaped, 

 funnel - shaped, cylindrical 

 or globular in shape, and 

 which consist of a large 

 central cavity, probably 

 filled with sarcode in the 

 living condition (fig. 28), 

 surrounded by a thick 

 wall of complicated struc- 

 ture. In the cup-shaped 

 forms (fig. 29, A) this 

 central cavity is widely 

 open above; but in the 

 globular forms, according to Billings, it communicates with 

 the exterior by but a small aperture situated on the 

 upper surface (fig. 28). The wall bounding the central 

 chamber is composed of (1) an external integument, (2) an 

 internal integument, and (3) an intermediate space crossed 

 perpendicularly by more or less closely approximated tubular 

 pillars (fig. 28, and fig. 29, c). Both the outer and inner 



Fig. 28. Diagram of the structure of Recep- 

 taculites, as it would be shown by a vertical sec- 

 tion of a perfect specimen, a, The aperture at the 

 summit ; b, The inner integument ; c, The outer 

 integument ; n, The usual position of the nucleus ; 

 v, The great internal cavity. The unshaded bands 

 running from the outer to the inner integument 

 represent the pillars. (After Billings.) 



