42 



cimens, in which, if finely preserved, the muscular plicae of the external 

 integument may frequently be traced, extending over the former, this, and the 

 following- joints. At its inner truncated point it has an elegant lip-like pro- 

 cess, similar to that noticed on the former joints, the plicae of both assuming 

 a perfectly conformable disposition, it has at its lower surface the transverse 

 perforated ridge, which also appears to exist at its superior surface. How- 

 ever, this last fact I can only advance hesitatingly on the appearance of a single 

 specimen, and beg to observe, that it does not accord with the organization 

 noticed in the Apiocrinites rotundus, to which I have found (speaking in general 

 terms) the present species strictly conformable in this point. 



The scapulae (PL. m. fig. 9. to 11.) rest on the subconcave surfaces of the 

 second costals, and being destined to support a row in which the division of 

 pieces is doubled, the upper surface is formed into an angular ridge, and the 

 lateral surfaces, in old specimens, are scarcely perceptible; so that in the ex- 

 terior circumference the margin of each joint is nearly triangular. At the in- 

 terior truncated point it is excavated, having in the centre a projecting pointed 

 process, on each side of which another excavation exists, behind which the sub- 

 triangular perforated ridge is placed in a slanting transverse direction. At 

 the lower surface a ridge also exists of a subtriangular figure, all the 

 angles are drawn in, and hence the joint has here again a convex form. The 

 scapulae evidently have lost all their analogy to the Apiocrinites, and point out 

 clearly in their formation a transition of organization to the next genus. 



On the five scapulae rest the ten first arm joints (PL. n. 1. and 2.) two of 

 them articulating to each scapula, viz. one on either slope of its superior angular 

 ridge, the outer circumference of each arm joint forms a parallelogram con- 

 tracted and drawn in at the angles, and hence has not unfrequently in young 

 specimens a tubercular elevation. 



To the first arm joint succeed several thinner joints, externally oblong, 

 straighten the lateral surfaces, and nearly flat on the upper and lower surfaces; 

 they are of a horse-shoe shape, and provided with tentacula on alternate sides. 

 Their number varies from six to eight, according to the age of the individual. 



The following joints which 1 should feel inclined to call those of THE 

 FINGERS (PL. n. fig. 1.) have sloping surfaces, and thin off on the opposite 



