Morse.} 340 [March 19) 
springing from these arms, are often highly and beautifully colored, 
sometimes each cirrus is banded with brown. 
In those with a closely wound spiral arm, as in Amphitrite ventri- 
labrum, the outer margin of the arm at the base of the cirri, is 
bordered by a delicate membranous frill, possibly corresponding with 
the calyx in Polyzoa, but precisely identical with the brachial fold in 
the arms of the Brachiopoda, as will be seen by reference to the sec- 
tions to be presently given. 
In the Brachiopods, the two arms springing from the fod are to 
be directly compared to similar parts just described in the worms. 
They also spring from a cartilaginous base, and sustain ciliated 
cirri, and in Lingula, Discina and Rhynchonella, they are developed 
in a closely wound spiral, as in Amphitrite. Furthermore in Rhyn- 
chonella, they can be unwound and protruded from the pallial cavity 
as I had the good fortune to observe in living Rhynchonella from the 
St. Lawrence.! (By instantly dashing the strongest alcohol upon the 
specimen, I was enabled to preserve it with the arms extended.) 
In Lingula the arms can be partially unwound, and what is very 
significant, the cirri in Lingula pyramidata are banded with light 
brown, as in certain species of Sabella. 
The cirri in Brachiopods 
Fig. 18. Fig. 14. show a rapid circulation 
through their transparent 
walls. They are employed 
to secure particles of food, 
which they convey to the 
mouth, and in every respect 
they are strictly identical 
with similar organs in the 
Annelids. A transverse sec- 
phitrite ventrilabrum, Fig. 13, 
and of the right arm of Lin- 
Transverse section Transverse section 
of arm of Amphi- of arm of Lingula guia pyramidata, Fig. 14, is 
trite ventrilabrum. pyramidata. here presented. These sec- 
ci. cirri. Bf. brachial fold. s. sinus. tions are, in each case, taken 
midway between the base and 
extremity of the arm. They much more closely resemble each other, 
than corresponding sections of two Brachiopods resemble each other. 
1 Am. Journ. Science and Arts, Vel. Iv, Oct. 1872. Otto Frederic Muller, ac- 
cording to Von Buch, also saw Rhynchonella gracefully uncoil its arms. 
tion of the right arm of Am- - 
