100 POTERIOCRINID^ EXTRACRINUS. 



points of bifurcation, and a few of the terminal joints of each ray being devoid of 

 tentacula, are alone free from these projecting supports. 



Parkinson, though unacquainted with the structure of the dorso-central plate of this 

 species, was quite correct in his description of the manner in which the raj's rest on the 

 upper surfaces of the larger series of perisomic plates, and which he has termed the 

 scapulae ; while Miller improperly represents the two joints of each main ray as a 

 portion of the body itself. 



The minor sulwlivisions of the rays varied considerably in number according to age 

 the smaller specimens having only five or six lateral branches emanating in each 

 leading ray, while in the adult animal they amounted to eighteen or nineteen, so that 

 if we multiply the lesser number by twenty, which is the number of the leading 

 branches, it follows that a full grown E.vlracrhnis Briarens has the surprising number 

 of three hundred and sixty rays, which give support to several thousand tentacula, each 

 furnished with appropriate muscles, all of which during life were capable of motion 

 according to the convenience, safety', and wants of the animal. Several terminal joints 

 of each ray, as represented in PI. 12, fig. 2. 1. are furnished with a small hook like 

 process, which resemble in form the feet of a caterpillar, and which there can be no 

 doubt were for the purpose of prehension, and in order that these organs might perform 

 their office, that of securing food and conveying it to the mouth, without obstruction 

 from the crowding of parts which might possibly interfere with each other, Ihe joints 

 on which th' se hooks occur are destitute of tentacula. 



The rays are long and tapering, and possessed the power of moving in every direction, 

 so that when they were spread arround with the tentacula filling the intervals between 

 them, they formed a complete net like apparatus through which nothing could pass 

 without coming in contact with some one or other of these delicate organs. 



In some specimens each ray has on its lateral margin several small tubercles, which 

 vary in form on almost every joint. 



The Tentacula. — With the exception of the cuneiform joints and the few that an 

 furnished with hooks at the extremities, each ray joint gives support to a jointed tenK 

 ulum. These gradually become finer and shorter in accordance with the decreai>e in 

 the size of the ray joints towards their terminal points. 



In Dr. Buckland's Bridgewater Treatise, PI. 53, fig. 17, a magnified extremity (>: 

 tentaculum, represents the two last joints as forming a delicate pair of pincers, we ht. >. 

 not been so fortunate as to detect these pincers in any of the tentacula, whicll we ha\ e 

 examiiiod, but we have constantly found them at the extremities of the rays. 



That portion of the body lying between the column and the first ray articulati .n^ 

 appears exceedingly diminutive, but when considered in relation to the whole of the 



