29 
The subtriangular ridge on the superior surface stands in 8 more slanting 
direction, and the superior circumference on the outerside of each arm joint, 
or that towards which the series arising from two scapule come together, is 
much decreased, thereby indicating that they will in the next series adhere 
no longer. 
The First FINGER Joint (Pr. vi. fig. 12. to 14.) is of a reniform shape, 
but slightly convex on its inferior surface, and concave on the superior. On 
the inside it is excavated, having slight lip-like processes, and behind these 
at its lower surface, a somewhat obliquely transverse subtriangular ridge, with 
a longitudinal groove at its apex for the admission of a similar but undivided 
ridge of the second arm joint. On the upper surface, a simple subtriangular 
ridge also appears, showing like that on the former, the aperture of the per- 
forating tube; this joint is entirely free at its sides, and is generally the first 
that sends off a tentacular process. I possess, however, a fine specimen of 
APIOCRINITE, perhaps the finest ever found (Pr, 1. fig. 2.) where this took 
place at the second arm-joint. In this individual, the tentaculum arises from 
the arm-joint on the right-hand side of the scapula, and from its left side; 
whereas in the case where thé first finger sends it off, it arises from the right- 
hand side of the joint over the left division of the scapula. The insertion 
of the tentaculum takes place in a part of the joint which is obliquely trun- 
cated on the right side near the superior surface, and forms a concave space 
traversed by a ridge, having in its centre a perforated cavity. 
The Srconp FINGER Joint (Pr. vr. fig. 15. to 17.) is also nearly reniform, 
excavated in the centre of its interior side, and truncated at both extremities, 
‘thereby giving insertion on the one side for a tentaculum, and on the other 
allowing freer scope to that arising from the first finger joint. That side which 
lies over the insertion of the tentaculum in the former joint, is somewhat 
thinner than the other, which-formation, as it is continued alternately through 
all the following finger joints, presents an admirable contrivance to furnish an 
additional dimension of adhering surface, and thence firmer . insertion to the 
tentaculum, without an undue increase in its size. On the inferior surface, 
where the second finger joint rests on the first, and also on the superior surface, 
it has a subtriangular ridge perforated in the centre. It also shows at its 
superior surface, numerous radiating strie, with interrupted ring-like mark- 
ings of growth similar to those in the former joints. 





