1873.) 341 (Morse. 
In Lingula the brachial sinus is quite large, while in Amphitrite, 
it is smaller. The brachial fold in the former is wider. ‘The differ- 
ences between the two, however, are differences of porportion of parts 
simply. In certain Polyzoa, just as in that curious worm, Phoronis, 
the cirri spring from a horse-shoe-shaped lophophore, hence they are 
called hippocrepian Polyzoa. In the early stages of Terebratulina, 
I have shown that at first the lophophore is circular, as in the lower 
Polyzoa, and afterwards the hippocrepian character reveals itself.! 
It was important to learn whether the mouth opened between the 
Fig. 15. 
st @ n ¢ of 
Longitudinal section of anterior portion of Lingula. 
Fig. 16. 
Qe 
TTass——22, 9 
\ 
XO 
Longitudinal section of anterior portion of Amphitrite ventrilabrum. 
ci. cirri. 6f. brachial fold. 
st. stomach. a. arm. 
c.c. cephalic collar or 
m. mouth. @. cesophagus. 
s. sinus leading to arm. 
cb. cartilaginous base of arm. 
pallial membrane. 
1 Morse. Early Stages of Terebratulina. Mem. B.S. N. H., Vol. 1. These obser- 
vations have since been confirmed by Dr. E. Ray Lankester in Annals Mag. Nat. 
Hist., February, 1878, on the young of Terebratula vitrea. 
