THE TRENTON CHINO ID, OTTAWACBINTJS 
5 
Of the two plates resting on x , that on the right (rt.) abuts 
on the shoulder of r. post. Rs, and on almost the whole of the 
left side of r. post. IB?!. Above, it supports the right lower side 
of a large plate. On the left it abuts on the other of the two 
plates (It.) It abuts, then, on five plates and is five-sided. 
The fellow plate on the left (It.) rests on x with a similarly 
curved lower margin, abuts on rt. with its side, and on two 
plates above with its two upper slopes. Its left side rests 
against a part of 1. post. Rs, and the whole of its ensuing brachial; 
but the plate curves inwards, and the line of junction with those 
ossicles is quite straight, so it may be that the actual margins 
of the plate are covered by the 1. post. arm. Therefore, though 
the visible portion of the plate is five-sided, the whole may 
perhaps have been six-sided. 
Resting above rt. and lt. } in the angle between them, is an 
irregularly hexagonal plate, 1*5 mm. wide, and of about the 
same height. Its right side abuts on r. post. IBr 2 , but a very 
small portion of its lower corner rests on IBr 1} and, if counted, 
would make the plate heptagonal. Above, it supports two plates, 
and its left side abuts on a plate which may have been hexa- 
gonal, but of which only three sides are seen. 
Five more plates of the anal tube are exposed on the outer 
surface of the fragment associated with the cup (Plate I, figs. 1, 
2.) They form part of three horizontal rows, but are irregular 
in size, shape, and arrangement. 
On the fragment comprising the cup it is not possible to see 
the plates that form the inner side of the tube. The shale 
fragment, however, contains at least three vertical series of 
plates, which probably belonged to the anal tube (Plate I, fig. 5). 
They are much lower and thinner than the associated brachials, 
and do not seem so closely united at the sutures. Their joint- 
faces seem to be bevelled towards the lumen of the tube, and 
this would have given the plates increased power of motion on 
one another. It appears, therefore, that the tube widened out 
a little distally, and that its skeleton was rather loose and 
flexible. 
The relations of the anal tube to the adjacent arms are of 
some importance. On the left, the tube-plates seem to bend 
round and inwards, so as to be quite independent of the adjoin- 
