HYDE: CAMAROPHORELLA. 45 
the crura. The lateral branches of the primary lamellae (pi. 6, fig. 
2, e) are short and stout. They are triangular in shape, the apices 
of the triangles uniting to form the stem. It is at their point of union 
(w) that the jugum rests on the elevated median septum. Each lateral 
branch is braced by a thickened ridge on the inner surface, that extends 
the length of the branch and onto the primary lamella. These braces, 
if such they are, are less marked in the adult than in the younger 
specimens. 
The stem (/) is variable but shows several constant features. In 
general it may be said to consist of a circular or elongate plate which is 
slightly concave toward the anterior margin of the shell, from beneath 
the upper edge of which (as oriented in the illustrations) an elongated 
plate projects which is sharply concave in the opposite direction. It 
is this latter plate that bifurcates to form the two accessory lamellae 
(b, b). The accessory lamellae originate at a considerable angle to 
the plane of the plate first mentioned, and make with each other an 
angle of between 60° and 75°. Each passes to the space between the 
primary lamella and the second whorl of the spiral ribbon lying 
between and parallel to them, as in Athyris, but reunites with the 
jugum at the base of the stem. 
This description of the jugum, which indicates a more complicated 
structure than that found in either ^Merista or ^Nleristella, has been 
given in the terms employed for those genera and for Athyris. In the 
two former, the lateral branches unite to form a short straight stem 
which in turn bifurcates to form the accessory lamellae. After de- 
scribing more than half a circle these reunite with the stem at its base. 
Nothing has ever been described which suggests that the structure 
of the loop of the Meristellinae was any more complicated than this, 
but this is probably due to lack of well preserved material. While, 
in general, the jugum of Camarophorella is built on the same plan, 
the structures that occur within this general plan are far more cpmplex 
than has been indicated above, and it is almost impossible to describe 
it as has been done above in the terms applied to the other genera. 
This complexity lies in that portion of the structure which is termed 
the stem. In order to present it properly it is necessary to describe 
its development in so far as it is known and to introduce at this point 
a brief discussion of the relation of the structures to corresponding 
structures in other spire-bearing forms. 
In all general descriptions of the structures occurring in spire- 
