ENCRINITES. 109 



the bottoms of the salt-water lochs which indent the 

 western coasts of Scotland. The Comatula is nearly 

 related to another free-moving Echinoderm, the 

 Euryale, a genus which has a very large geographical 

 distribution. One living species of Euryale, called 

 palmifera (Fig. 88), is evidently nearly related to the 

 common brittle-stars (Ophiurida), which do not pos- 

 sess the ordinary water-vascular system, and are 

 covered with rows of limy plates. The commonest 

 of our British species is Ophiura granulata (Fig. 90). 

 Thus we may pass, as regards their external forms, 

 from true living crinoids, stalked and jointed, to 

 others which are Crinoids only during the earlier part 

 of their lives ; thence to free-crawling Comatulas and 

 Eiiryales, and through the latter to the brittle-stars. 

 This remarkable relationship is still further indicated 

 by the external limy plates which cover or otherwise 

 enter into the structure of Crinoid, Feather-star, 

 Euryale, and Brittle-star alike. A similar blending 

 of the external shapes of allied forms may be seen 

 in another large group of Echinodermata the star- 

 fishes and sea-urchins. Thus, beginning with As- 

 terias (noted for the body and arms being covered 

 with limy plates), we pass on to the Cushion-stars, 

 where the arms appear to have been stretched along 

 their sides till they have grown together. Thence 

 we pass by such forms as Scutella and Spatangus, 

 until we come to the true and abundant sea-urchins 

 (Echinus), so that the wide space between the Encri- 



