~] 
ba | 
VoL. 2] Ritter—The Pelagic Twnicata. 
same interval, excepting that the interruption of the sixth on the 
ventral side is much greater than that of any of the others. Two 
muscles, the one dorsal, the other ventral, probably representing 
lip muscles of other species, but rather remote from the branchial 
orifice, meeting in an acute backwardly directed angle on each 
side. A short, semi-lunar scrap of muscle on each side, close 
within the antero-lateral angles. The posterior orifice small, 
terminal in position, with rather distinct dorsal and ventral lips, 
each containing a delicate muscle. 
Endostyle straight and slender, extending nearly the entire 
length of the body, but terminating posteriorly somewhat short 
of the nucleus. Gill likewise peculiarly long and slender, extend- 
ing back of the nucleus, hence beyond the posterior end of the 
endostyle. Hypophysis simple, narrowly elliptical, projecting 
but shghtly into the pharyngeal cavity, situated exactly in the 
sagittal plane. Ganglion rather small and eye spot seareely pig- 
mented. Nucleus small, situated very far back in the base of 
the posterior ventro-median process of the body. A pointed 
outpocketing of the mantel projecting behind the nucleus into 
the process of test. The stolon beginning far back and extend- 
ing somewhat backward to wind around the nucleus from right 
to left. 
Fig. 21.—8S. zonaria-cordiformis, aggregate generation. 
(b) Aggregate (sexual) generation—Fig. 21. Body firm, 
from the hardness of the comparatively thin test; irregularly 
cigar shaped in general outline. Branchial orifice fully on the 
dorsal side and looking directly upward, its two lips prominent 
and equal in size. Posterior end produced into a broad process 
of varying length, in some zooids it equaling half the length of 
the body, while in others it is much shorter, and in still others 
almost wholly wanting. In all the specimens that have come 
