APPENDIX TO CHAPTER XIII 203 



sort of tail (Caudina, 1 Fig. 189) occurs on the Massa- 

 chusetts coast. A worm-like form, but with a beautifully 

 transparent skin (Synapta, 2 Fig. 190), is found in sandy 

 beaches from Massachusetts to New Jersey. 



The Crinoids, 3 or sea-lilies, are familiar as fossils to resi- 

 dents of New York State and the Ohio and Mississippi 

 valleys. The living animals are less often seen, for they 

 are inhabitants of the deep sea. They have a cup-like 

 body, with the mouth at its centre directed upward, and 

 surrounded by tentacles (Fig. 191). The cup is either 

 borne on the end of a long stalk or is unstalked. The 

 former condition is more usual among the fossil species. 



APPENDIX TO CHAPTER XIII 



KEY TO THE PRINCIPAL CLASSES OF ECHIXODERMATA 



a\. Sessile ; mouth turned upward ; body calyx-shaped Crinoidea 



(Sea-lilies) 



a. Not sessile. 



61. Body short ; skin hard, containing calcareous 

 plates ; mouth directed downward ; madre- 

 poric plate present. 



Ci. Body with arms which carry a longitu- 

 dinal series of plates. 

 d\. Arms with ventral furrow . . Asteroidea 



(Starfish) 



d%. Arms without ventral furrow . . Ophiuroidea 



(Serpent stars) 



1 cauda, tail. 



2 <rvvaiTT6s, fastened together ; from o-i/v, with, and ATTTW, to fasten. 



3 Kpivov, lily ; e!5os, form. 



