10 PLATVCRINID.E. PLATYCRINITES. 



of single joints for a short distance above tlie points of bifurcation, which structure is 

 succeeded by a double series of joints beautifully articulated into cacli other, the salient 

 angles of one set enterhag into the retmng angles of the adjoining set. (Vide PI. 1.) By 

 this arrangement the greatest possible flexibility, combmed with the requisite strength, 

 was secured to the animal, which must ha\e relied in a great measure on quickness of 

 action and a delicate sense of touch for seciu-mg its food. 



The inside of all the rays were sulcated tlu'oughout tlieu- whole length : in these sulci 

 the muscles which iniparted motion to the extremities played. An integument, plated 

 wdth exceedingly minute plates, extended over and protected the softer parts contamed 

 in the sulci fi-om injury. It is not improbable that cilia, almost imperceptible fi-om 

 theii' minuteness, were ranged along the lateral fimbriate \seh which fringed the 

 pinnae, whereby the animal, by their extreme sensibility, was enabled to detect minute 

 objects in contact ■with the rays or tentacula. 



The cunieforni joints of the rays were doubly sulcated, to allow a free passage to the 

 muscles where the bifurcations take place. PI. 1. ;•. The whole structure of the rays, 

 the joints gradually diminishing in size to their extremities, with the inner plated 

 integument, exhibit many beautifid contrivances to produce that degree of flexure which 

 is so conspicuous in the rays of the Crinoidea. 



There is reason to suppose that the joints of the rays were not wholly calcareous any 

 more than the column, but that the indurated matter was arranged in a tubular manner 

 throughout their substance. 



The rays in this species are uniform in length. 



The Tentacula. — From the outer side of each ray joint, PI. 1. s. proceeds a single 

 tentaculum, which is composed of numerous joints. These plumose appendages vary in 

 full sized specimens, from half to three quarters of an inch in length, and gradually 

 diminish in tliickness to their extremities. 



The tentacula become perceptibly closer to each other as they approach the extreme 

 points of the rays ; this is owing to the gradual diminution in the size of the ray joints 

 themselves, each of which having a single tentaculum attached to it, they, as a matter of 

 course, become more closely set towards the ends of the rays. 



The tentacida are composed of numerous joints, whose imier smfaces are finely sulcated 

 longitudinally. The softer substance filHng the sulci, as in the rays, was probably 

 protected by a x'lated integument, which effectually secured it from external injiuy. 



The extremities were moved by the muscles which occupied the jjei-forations and 

 sidci, now seen m the inchu-ated frame work of the animal, and not by a muscidar 

 integument which Miller assumed covered both the interior and exterior siu-faces, 

 "eff'ecting by its contractile power the movement of the arms." 



That the exterior surface was covered by a cortical envelope, or recticulated tissue, is 



