HYDE: CAMAROPHORELLA. 47 
each from a type in which the stem M'as simply bifurcated at the free 
end. 
Nothing, to the writer's knowledge, has ever been produced to show 
the development of one of these juga from the earliest stages of an 
indi^'idual to the adult. The reason for this is, of course, the great 
difficulty of obtaining suitable material. If it could be shown that in 
the development of the individual, there is a series of metamorphoses 
more or less parallel to the supposed phylogenetic series outlined 
above, the evidence would be very strongly in favor of, and to some 
persons, proof of the approximate line of descent. 
The Sciotoville material does not offer, as yet, by any means a 
complete series, but those stages that are at hand indicate a different 
method for the formation of the jugum, in ontogeny at least. The 
youngest indi^idual in Avhich the structure was studied is 8.5 milli- 
meters in diameter and has five whorls in the spiral. It is readily 
seen that it is in a comparatively late stage of development. This 
specimen is shown in figure 51 (pi. 10), which is magnified eight diam- 
eters. The jugum is completely formed and shows very strikingly 
a featvire that is persistent in all the adults, as far as can be observed, 
but is much less pronounced. This is the distinct saddle formed by 
the union of the lateral branches or jugal processes of the primary 
lamellae. It is very similar in form and position to the "saddle" of 
Athyris (pi. 6, fig. 1) but heavier and relatively reduced in size. Strong, 
brace-like ridges extend from the somewhat flattened posterior surface 
of this saddle onto the primary lamellae, but it is doubtful whether their 
function is solely to strengthen the structure. It is far more likely 
that they are developed in response to the A-shaped apex necessitated 
by the habit of resting the jugum on the tip of the median dorsal sep- 
tum and without which rigidity would be impossible. 
The noteworthy fact is that the "stem," so called for convenience, 
is not a continuation of this saddle. Although in contact with its 
anterior surface, it is not in such intimate contact but that the suture 
between the two is most striking. The whole suggests that the jugum, 
as represented in this specimen, consists of two separate parts, the 
saddle and the remainder of the jugum, which has been laid upon it 
as a separately formed plate. That is, the portion referred to as the 
stem and the two accessory lamellae formed by its bifurcation, to and 
including their point of union with the base of the "stem," have not 
been formed by a gradual splitting of the stem, a recurving and reunit- 
