HYDE: CAMAROPHORELLA. 49 
phore maintaining their original contour, while the folds on the other 
side changed to such an extent during development that the original 
structure was either resorbed or covered over. Or, the folds of the 
lophophore at the initial period of spiculization may have been such 
as to cause the plate to be laid down in a form very like the ones ob- 
served, the outer margins of the lamellae being fused with the sides 
of the saddle from the earliest stages. To the writer, the latter seems to 
have been the more probable mode, in view of the fact that in the 
earliest known stages, including the smallest one just mentioned 
(which was broken), there is nothing to suggest that the former may be 
the correct explanation. 
The last structure to be described in connection with the jugum is 
the plate-like expansion on the anterior surface between the saddle 
and the point of separation of the lamellae. It may be broadly 
expanded and more or- less circular as in figure 45 (pi. 9). In this 
specimen it is nearly flat but slightly concave. Or, as in figures 48 
and 49 (pi. 9), and 53 and 55 (pi. 10), it may be relatively narrower 
and much more concave. It is not certain that either is especially 
characteristic of certain stages of growth. It is always slightly wrinkled 
parallel to the edges. In all specimens sufficiently well preserved 
to admit of judgment, six in number, it has every appearance of an 
extra plate laid upon the jugum. At the ventral end (upper in draw- 
ings) it rests on the united secondary lamellae, the strongly convex 
surface of which is plainly visible for one fourth or one half the length 
of the plate. At the dorsal (lower) end the edges are distinctly fused 
to the outer surfaces of the secondary lamellae near their point of 
union with the saddle. Figures 52 and 55 (pi. 10), show the relation 
well. As viewed from the under or posterior surface, the line of con- 
tact between this plate and the lamellae at both its dorsal and its 
ventral ends is marked by a deep suture. Near the center of the plate, 
however, at the tip of the saddle it is more intimately united with the 
lamellae. 
It is not certain whether this represents a period of spiculization 
in a portion of the lophophore subsequent to that by which the body 
of the jugum was formed and is, thus, really a secondary plate, or is 
due merely to certain peculiarities in the lophophore which have 
caused it to take the form of a separate plate. It is not seen in the 
young specimen shown in figure 51 (pi. 10), but only a small portion 
of the anterior surface of the jugUm is here visible. Furthermore 
