104 HYATT, 



igastric cavity (PL 11, fig. 1, PI. 12, fig. 2, PI. 13, fig. 15, 

 O'). They divide near the bases of the arms into two 

 broad bands, accompanying the clear tentacular spaces 

 across the bend of the "horse-shoe" and around the cesoph- 

 agus. The outer tentacular bands incline the tentacles 

 outwards, or side wise, the inner tentacular bands bend 

 them towards the centre of the lophophore. 



The epistome is provided with three interior muscles, 

 a small central muscle on the side next to the mouth, and 

 two larger ones on the opposite or dorsal side (PI. 11, 

 fig. 1, PL 13, fig. 14, P, F). The former has its base 

 close to the oesophagus, and is attached by the posterior 

 extremity to the inner side of the border of the epistome 

 on the median line, the base and attachment being quite 

 broad and of about equal size. The two latter have their 

 bases fixed to the lophophore close to the roots of the ten- 

 tacles, thence they spread in fan shaped masses on either 

 side, sending muscular bundles to nearly the whole of the 

 inner surface of the border of the epistome. The single 

 median muscle produces the ordinary jerking action of the 

 epistome, and the two lateral muscles elevate it, or modify 

 the outline of the border. These muscles are figured as 

 one by Prof. Allman, probably owing to his having vie wed 

 them laterally, mistaking the two lateral bands for a sin- 

 gle muscle, and overlooking the median band which in 

 most lights is not visible from the side. 



NERVOUS SYSTEM. 



Viewed from the dorsal side, the nerve mass of Fred- 

 ericella is irregularly elliptical, or orbicular, and when ex- 

 panded, lies flat against the oesophagus (Fig. 9). When 

 contracted the anterior is drawn up in close proximity to 

 the posterior end, giving the peculiar heart-shaped or ro- 

 tund aspect, from the side, which has been previously He- 

 scribed and figured by Dumortier and VanBeneden, and 

 Prof. Allman in Fredericella sultana.* Hancock, how- 



* DUMORTIER and VAX BENEDEX. Op. cit. Nouv. Mem. Acad. d 

 Bruxelles, Tom. If?. Complement pi. 3. ALLMAN. Op. cit. pi. 9. 



