52 
pointed termination to the interior truncated and excavated point, forming two 
slanting sides for the adhesion of the first arm joint. Each of these are tra- 
versed by a perforated ridge running in a slanting direction from the interior to 
the exterior point. 
The Arms.—The ten arms proceeding from the fivescapule, (two from each) 
are each formed of five joints nearly of an horse-shoe figure, sending off from 
their alternate sides the tentacula. The superior surface of the first arm joint _ 
(Pu. 11. fig. 4.) and the inferior of the second, are subconcave, perforated in 
the centre, smooth, with fine radiating ridges at the circumference, and want 
the transverse subtriangular ridge which exists in the following arm and finger 
joints. In these it traverses the superior surfaces (PL. 11. fig. 1. to 3.) in an 
angle from near the place where the tentaculum sets off to the opposite exte- 
rior circumference, and at the inferior surface in an opposite direction to the 
former. On the inside the joint is excavated in the centre in a sharp angle, 
it is thicker on the side which sends off the tentacula, being there cut in an ob- 
liquely transverse section, of which the lower portion shows a ridge, the mark of 
articulation, whilst the upper forms a slender lamina, The projecting point on 
the other side is slantingly cut off to permit room for the action of the tentacr- 
lum from the joints below it. There are also several irregular rug on the ar- 
ticulating surfaces, serving as points of adhesion to the muscular integument. 
The upper or sixth joint of the arm (PL. 1. fig. 11. to 14.) resembles in 
figure the scapula; this, and those other joints bearing an analogy to it, Ihave 
distinguished by the name of cuneiform joints, from their upper surface posses- 
sing two opposite slopes, and, like a wedge, interrupting the further continu- 
ing of a series of joints, and rendering it dichotomous. 
The cuneiform joints never send off a tentaculum, and to obviate the 
interruption or vacuity thus occasioned in the beautiful net-like apparatus 
displayed when the hands and fingers with their tentacula are expanded, the 
number of joints below the cuneiform one generally varies in the hands; thus 
affording an opportunity for the insinuation of the tentaculum arising from 
the neighbouring hand, into the vacant place if required. 
The Hanp and Fincers. (Pu. 1.) These are twenty in number, two pro- 
ceeding from the cuneiform joint of each arm. ach series proceeds through 
about eight or nine joints, and then by means of another cuneiform joint gives 
