.ANDREWS: ANNULUS VENTRALIS. 457 
vestibule extending over to the right as a flattened pocket that opened 
downward in the anterior part of the depressed area somewhat under 
the edge of the cushion. In this specimen it opened under the cushion 
on the left while in the specimen shown in 29 and 31 (pi. 47) it was on 
the right, these being two cases of right- and left-handed symmetry. 
Posterior to this vestibule, which is empty (pi. 46, fig. 23), followed 
a semicircle of tube full of flaky material which was the wax-like 
substance that plugged up the cavity as far back as to the median line 
at the end of the second semicircle. The two following semicircles, 
to the right and then to the left, were full of sperm which is represented 
by dotted areas in figure 23. The sperm tube ends in a slight enlarge¬ 
ment of the median line and just posterior to this is a small and appar¬ 
ently isolated pocket of sperm. The exoskeleton walls of this long, 
much bent trumpet are seen to be rather thick but relatively much less 
so than in C. affinis (pi. 43, fig. 5). 
The relationship of the cavity of the trumpet and the zigzag suture 
was made out in such ventral views of translucent annuli as that 
shown in figure 21 (pi. 46), which is a specimen having the same 
symmetry as the one in figures 29 and 31 (pi. 47). Here certain areas 
were opaque, that is, all the posterior half of the annulus to some 
extent and the posterior faces of the cushions, where seen through 
their depths. Showing through the translucent floor of the central 
depressed area, the thick walls of the trumpet tube are seen enveloping 
its cavity and anteriorly passing over into continuity with the exoskel¬ 
eton of the floor of the depressed area. On the translucent surface 
of the annulus runs the zigzag suture, coinciding in its sharp turns 
with the smooth curves of the overlying trumpet tube. From the 
posterior end forward, we see a blunt median ending of the tube above 
the median line of the suture, an arc to the left alongside of the second 
line of the suture, an arc to the right and anteriorly alongside of the 
third line of the suture, an arc to the right alongside of the fourth line, 
a transverse and posterior arc along the fifth line, and an arc on the 
right of the sixth line. The two last arcs are but the walls of the 
vestibule, or flaring flattened mouth of the trumpet, where it opens 
upward in the figure into the most depressed part of the ventral sur¬ 
face of the annulus. The two anterior lines are but parts of the rim 
of the vestibule. The four other lines are the tightly closed mouths 
of curved clefts leading to the arcs of the tube and thus putting the 
whole length of the tube into morphological communication with the 
exterior. 
