420 S. W. Ford—New species of Primordial Fossils, 
readily distinguished from the ventral by the presence of two ob- 
scure ridges radiating from the nucleus to the margin, and en- 
closing a triangular space along the central portion of the limb, 
The two limbs are so situated relatively to each other as to 
e 
give to the base of the operculum a curvature equal to that 
mb. All of these ridges are widest at their junction with the 
margin. They severally terminate in the central pit, and 
divide the interior into four unequal parts. ; 
he surface of the operculum is covered with fine concentri¢ 
strize, from 8 to 10 in the space of 06 of an inch. Along wi 
these there sometimes occur coarser lines of growth. The in- 
terior is both radiately and concentrically striated. The con- 
centric lines are mostly coarser, fewer in number, and far less 
regularly disposed than those on the outside. _ The radiating 
ines are very numerous, and with the concentric lines give to 
the interior a singularly reticulated appearance under the mag- 
nifier. They are barely visible to the naked eye, ae 
This is a well marked species, and offers but little varla- 
tion of form. It is closely related to Hyolithes communis Bil- 
Billings. . 
The specimens were collected by the writer. 
: * Canadian Naturalist, vol. vi, p. 214, December, 1871. 
