50 INVERTEBKATE ANIMALS. 



Group 141. Genus PALMIPES (Linck), and allies. 

 In this group tbe arms or rays are slender, so that the 

 web which joins them constitutes the chief part of the 

 body. Palmipes, the Bird's-foot Sea-star, the thinnest 

 and flattest of the order, ranges from the Arctic Seas to 

 the Mediterranean. Estimated number of species : 

 recent, 47 : British, 1 ; fossil, 7. Higher Crag. 

 iy Examples of Culcita, Asteriscus, Oreaster, &c. 



Group 142.— Genera ASTROGONIUM (Muller), and 

 GONIODISCUS (Muller). The long, sharp, and 

 strong spines conspicuous in some of the species of 

 this group serve to protect the animal from the attacks 

 of enemies, or from the effects of sudden concussions. 

 The animal can lower its spines in any required direc- 

 tion, as river steamers lower their funnels when passing 

 under a bridge. Estimated number of species : recent, 

 30 ; British, 2 ; fossil, 34. Chalk and Higher Crag. 

 H Examples of Paulia horrida, Antennea, &c. 



Group 143. — Genera ASTEROPSIS (Muller), and 

 ARCH ASTER (Muller). Star-fishes, writes A. 

 Agassiz, have a singular mode of eating : they place 

 themselves over whatever they mean to feed upon, — as for 

 instance a cockle,— the back gradually rising as they arch 

 themselves above it ; they then turn the digestive sac 

 or stomach inside out, so as to enclose their prey com- 

 pletely, and proceed leisurely to suck out the animal 

 from the shell. Estimated number of species : recent, 

 11 ; fossil, 2. Green-sand. 



