SAND-STAIiS AND STAR-FISHES. 



Ill 



'beach. It is variable in color, but beautifully spotted with 

 pale and brown, its general hue being a brick-red. Am- 

 phiura squamata Sars has long slender arms and is 

 white ; it lives below tide-marks. The basket-fish, me- 

 dusa's head, or Astropliyton 

 Agassizii Stm., is of large 

 size, the disk being two in- 

 ches across, and the arms 

 subdividing into a great 

 number of tendril-like 

 branches. It lives from ten 

 to one hundred fathoms in 

 -the Gulf of Maine. 



Ophiurans are widely dis- 

 iributed, and live at depths 

 between low- water mark and 



-two thousand fathoms. Fos- TiS.l%—OpMopholisbeais,coiamonSmA- 

 • 1 /-. 1 • T J star. — After Morse. 



sil Ophiurans do not occur 



in formations older than the Upper Silurian, where they are 

 represented by the genera Protaster, Palmodiscus, Acroura, 

 siaA Eucladia ; genuine forms closely like those now living 

 appear in the muschelkalk beds of Europe (Middle Trias). 



Order 2. Aateridea. — In the true star-fishes the arms are 

 direct prolongations of the disk, and the stom.ach and 



O ^ A 



Fig. 73.— Three forms of Star-fish, A, B, C, eeeu from above, bhowm^ the duferent 

 ■developmeiit of the anihulacral and inleramhulacral aroaw. The ambulacra are hidi- 

 ;ated by rows of doty; o, mouth; r, arms; ir, intermdia] or iuturambuiacral areas. 

 € Fterasttr; B, GonionHscim; A, Aateiiscus. — After Gegeiibaur. 



ovaries or spermaries project into tliem^ and there is a deep 

 ^mbulaeral furrow, while the inter am bulacral spaces vary 

 much in development (Fig. 73) ; the feet are provided with 



