ECHINODEKMATA. 



137 



Fig. 57. 



present extremely rare : one 

 minute species only has been 

 detected in our own seas ;* 

 while specimens of larger 

 growth, such as that repre- 

 sented in the engraving, deriv- 

 ed from tropical climates, are 

 so seldom met with, that it is 

 fortunate that one or two ex- 

 amples have been found to 

 reveal to us the real structure 

 of a race of animals once so 

 common, but now almost com- 

 pletely extinct. The body of 

 the Encrinus (Jig' 57, a) (or 

 pelvis, as the central portion 

 of the animal is termed by 

 geological writers,) is com- 

 posed of numerous calcareous 

 plates, varying in shape and 

 arrangement, so as to become 

 important guides to the identification of fossil species ; from this 

 central part arise the large rays (b, b), each furnished with a double 

 row of articulated appendages, which, as well as the arms, are, no 

 doubt, instruments for seizing prey and conveying it to the 

 mouth, situated in the centre of the body near the point a. 

 This part of the animal, when found in a fossil state, from its re- 

 semblance to a flower, has received the common name of a " lily- 

 stone." 



The body above described, with the rays proceeding from it, is 

 supported upon a long pedicle (e), composed of numerous pieces ; 

 and, upon the sides of the stem, similarly constructed filamentary 

 branches are fixed (d, d) at equal intervals. The skeleton of an En- 

 crinite consists, therefore, of thousands of regularly shaped masses 

 of calcareous earth kept together by the living and irritable flesh 

 in which they are imbedded, and it is to the contractions of this 

 living investment that the movements of the animal are due ; but 

 after the death of the creature, and the consequent destruction of 

 its soft parts, the pieces of the earthy frame-work become sepa- 

 rated and fall asunder, forming the fossil remains called " Troeki," 



* Thompson (J. W.), Memoir concerning the Pentacrinus Europaeus ; Cork, 1827, 4to. 



