FOSSILS OF 1 THE LOWER SILURIAN. 



POGONIP GROUP. 



RHIZOPODA. 

 , Genus EECEPTACULITES Defrance. 



Receptaculites mammillaria 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 mm , in examples from 40 mm to f>0 mm 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 l mm , which gradually increases to 

 2.5 mm 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 mm , that appear to be made up of little projections or stolons uniting 

 the tubes on the upper annulations. 



5 c D w 65 



