490 PROCEEDINGS: BOSTOX SOCIETY NATURAL HISTORY. 
orifice, which in full expansion often becomes roundish. The branchial 
tube has about the same diameter, and is short cylindrical, with six 
short papillae around the 
orifice. In contraction the 
tubes form low verrucae. 
"When living the color 
of the body is translucent 
dull greenish or olive, be- 
tween the tubes usually 
more or less ferruginous 
brown or russet; on the 
sides the viscera show 
through as dull orange-col- 
ored and darker blotches. 
"One of the larger speci- 
mens was, when living .45 
of an inch long; height .35; 
length of branchial tube 
.10; diameter .10; distance 
between bases of tubes 
.08." 
There are specimens in 
the collection exceeding 
these dimensions. One from 
Casco Bay, Me., measures 
16 mm. long, 13 mm. dorso- 
ventrally (excluding the 
siphons), and 11 mm. from 
side to side. The specimens 
vary greatly in their exter- 
nal appearance and shape, 
some being attached by a 
broad area and considerably flattened, others are more nearly round. 
Some are very smooth externally, others quite rough and with much 
adhering sand and foreign matter. Often the siphons bear on their 
outer surface a few short spiny processes. Some of these may also 
occur on other parts of the body. 
Musculature of mantle weak, and on most parts of the body difl'use, 
consisting of fibers more or less isolated or grouped into only the nar- 
Text-flg. 11. — Caesira cilrina (Alder and 
Hancock). Part of branchial sac. X 15. 
