138 BULLETIN OF THE 
Torus angularis and Teeth. — These structures arise later than the first 
pair of adambulacral plates, but develop quite early in the growth of the 
young Ampbiura. They form as independent calcifications. The torus 
is at first an elongated plate or bar, which later becomes semicircular. In 
Fig. 20 this plate is represented as perforated and reticulated. It ap- 
pears that the teeth are not separate centres of calcification, but grow out 
directly from the adoral region of the torus. The calcareous deposit 
which enters into their formation has the form at first of a reticulated 
perforated triangular plate. 
B. PLATES OF THE ARMS. 
The plates of the arms are the following :— 
1. Terminals, ¢p. 
2. Side plates, dp. 
3. Ventrals, v. 
4, Dorsals, d. 
Terminals. —-'The terminal plates (tp) which lie at the aboral extrem- 
ity of the arms have been described by many observers. These plates 
have been confounded by many writers with the radials. Ludwig * first 
distinguished them from what are already described as the radialia or 
primary radials. The fact that certain plates early formed in the 
young Ophiuran were pushed out by a growth of new plates was known, 
but in all cases these plates were regarded as “ primary” plates and were 
in some instances morphologically misinterpreted. In Amphiura Krohn+ 
has figured the terminal plate, but gives it no special description. Max 
Schultze ¢ recognized the fact that the terminals belong to the arm proper, 
and correctly designates them as the “erste Anlage der Arme.” A. 
Agassiz § observed the terminal plates in an Ophiuran, probably Ophi- 
opholis, which he referred to Amphiura. He regards them as the first 
of Amphiura, it might be supposed that he does not consider these early formed 
plates as primary plates of the test. In strict language they are mouth-plates, but 
are so early formed in the larva that they may be regarded as primary plates. Asa 
question of opinion I think they ought to be mentioned in a discussion of the homol- 
ogy of the odontophore. 
NOD. Cite De LSie 
+ Op. cit., Pl. XIV. Fig. 1, 0; p. 342. 
t Op. cit., Pl. I. Figs. 4, 5, c. In Fig. 6 they are lettered f He does not seem 
to have connected Plate c, Figs. 4, 5, with f, Fig. 6. 
§ Op. cit., p. 20, Fig. 32, y. 
