134 



OUR COMMON BRITISH- FOSSILS. 



surfaces by their means. They are hundreds in 

 number, but all are fashioned alike, and the mechanism 

 which renders them locomotive organs is of the most 

 wonderful character. These feet are termed by 

 naturalists ambulacral, but I defer a detailed descrip- 

 tion of them until we come to speak of the sea- 

 urchins. The stomach of this kind of star-fish is 

 continued up each arm, and this fact naturally groups 



Fig. III. — Fossil " Brittle Star-" fish {Protaster Miltoni) (Upper Ludlow rocks, 

 Leintwardine). 



together genera which may have a greater number 

 of arms than five, and the "sun-stars" (Solaster), 

 which have twelve. 



In the "brittle-stars" {Ophmridea), on the con* 

 trary, the stomach does not extend up the arms, 

 cilthough the nervous branches of the ganglion sur- 

 rounding the mouth do. The " sun-stars " have only 

 tivo rows of suckers, whilst the " five-fingers " possess 



