2b'2 ZOOLOGY 



the disk and a single arm. Thus one may find a starfish with 

 three or four rays, or with, a small ray between normal-sized 

 ones. Not all al.)normalities seem to be the result of mutila- 

 tion, however ; for example, sometimes two arms seem to be 

 fused (Fig. 241). 



Fig. 242. — CrlbcUa sanguinolc/da. Nat. size. From Lcunis. 



Other Starfishes. — Besides Asterias vulgaris there are over 

 five hundred species of starfishes. In some of these — as in 

 Asterias — the skeletal plates of the skin make a network ; 

 in others they form a solid calcareous covering.^ 



1 To thf first das.s belong, besides Asterias vidgaris, Asicrias ochracea, 

 which occurs commonly on the Pacific coast from Sitka, Alaska, to San Diego, 

 California.. This has a much thicker, more solid skin than the Atlantic species. 

 A. gigantcd attains a diameter of over two feet. As an example of the second 

 class may l>e cited CrihcUa sanguiiiolenta (Fig. ISl), a smooth, leathery, 

 blood-red starfish, about ten centimetres in diameter, which, next to A, 

 vulgaris, is our commonest Eastern species. 



