66 University of California Publications. [ ZooLoGY 
asymmetrical, the anterior being to the right, the posterior to 
the left, or vice versa (the one figured is anterior process right, 
and posterior left). Length of large specimen, 25 mm.; usually 
smaller. Branchial orifice inclined distinctly upward, though 
not wholly dorsal. Atrial opening nearly directly backward. 
Lips of branchial orifice not prominent, dorsal deeper, but ven- 
tral extending farther forward in correlation with the obliquity 
of the orifice. Atrial orifice scarcely lipped. Body muscles 
Fig. 13.—S. fusiformis-runcinata, aggregate generation. 
seven, never interrupted on dorsum, and never continuous across 
the ventral side. Anterior four, and posterior three, confluent 
on dorsum. Last of anterior group and first of posterior group 
confluent laterally, but the two disconnected at ends. Posterior 
two, the sixth and seventh, confluent well down the side, the two 
separating, the sixth to pass in front of the nucleus, the seventh — 
behind it. The seventh usually confluent with a smaller muscle 
belonging to the atrial orifice. A large muscle band in the dorsal 
lip of the branchial orifice a short distance back from the edge, 
a delicate one at the very edge, and a broad band in the ventral 
lip. An angular muscle band at the angle of the branchial ori- 
fice on each side, its angle directed toward the angle of the orifice, 
and its two limbs directed, the one ventrad, the other dorso- 
posteriad. Endostyle slender, extending far forward under the 
ventral lip to a level with the ventral ends of the sixth muscle, 
some distance in front of the nucleus. Gill rather shorter, rela- 
tively, than in the solitary generation, and making a wider angle 
with the endostyle. Anterior end about middle of the interval 
between the dorsal lip and the anterior group of muscle bands, 
posterior end at the nucleus, hence some distance behind the 
posterior end of the endostyle. ‘‘Nucleus’’ rather small, com- 
pact, egg shaped, situated far back, projecting somewhat from 
