FOSSILS OF THE LOWER SILURIAN. 
POGONIP GROUP. 
RHIZOPODA. 
Genus RECEPTACULITES Defrance. 
Receptaculites mammillaris Newberry. 
Plate xi, fig. 11. 
Receptaculites mammillaris Newberry, 1880. Name proposed in manuscript. 
There is quite a range in the forms taken by this species, the most 
prevalent of which is an inverted cone with a deep depression on the upper 
surface, the height being to the diameter of the summit as four to five. 
In the more expanded examples, with the height and diameter as one to 
two, the base is small, and when the specimens are reversed, form a nipple- 
like projection on the’summit of the broadly rounded surface. The walls 
have a thickness of about 18™", in examples from 40™™ to 50™™ in diam- 
eter. 
The outer surface or ectorhin is formed of rhomboidal plates arranged 
in radiatingly curved lines crossing each other obliquely; the plates near 
the base have a greater diagonal axis of 1™, which gradually increases to 
2.5™ in the plates towards the summit; the only surface character preserved 
is a slight depression in the center of each plate. The cylindrical tubes 
uniting the ectorhin and endorhin have the characteristic construction of such 
tubes in Receptaculites near the base, but have not the connecting stolons 
or tubes between the constrictions and the ectorhin. Their absence may 
be owing to the imperfect condition of the specimens examined. Along the 
upper portion of the tubes there is a series of annulations, ten in a distance 
of 6™, that appear to be made up of little projections or stolons uniting 
the tubes on the upper annulations. 
5cDW 65 
