STAB-FISHES 



549 



rayed ones in size and structural details. One from Van- 

 couver Island lias seven regular rays. 



Asterias epichlora (Brandt). Although this species 

 was originally described as five-rayed, its normal, or most 

 common condition is six-rayed (var. ahiskensis Ver., var. 

 nov.), with a more or less evident median dorsal row of 

 small capitate spines, and numerous smaller capitate 

 spines forming a reticulated pattern over the back. 1 " ( )ne 

 specimen from Victoria has seven rays, due to the forking 

 of one ray about at the middle; another is regularly eight- 

 rayed. The five-rayed form is, perhaps, rather too fre- 

 quent to be classified under Teratology, but in the several 

 collections of epichlora examined by me, at least !»0 per 

 cent, of the specimens were six-rayed. The young, carried 

 by six-rayed adults, were all six-rayed. 



Ctenodiscus crispatus. Of this abundant species I have 

 from Xew England a considerable number of regular four- 

 rayed specimens. The few west coast specimens are five- 

 rayed (fig. 3, a,b). 



Significance of Radial Variation; a Problem in 

 Evolution 



When we consider the geological antiquity and remark- 

 able persistence of the five-rayed condition 11 in echino- 

 derms, generally, it seems remarkable that so many 

 genera and species of existing starfishes should have ac- 

 quired the peculiaritv of having higher numbers. 



All the classes of echinoderms, except perhaps holo- 

 thurians, had attained highly organized and specialized 

 conditions even in the Ordivician period. With the ex- 

 ception of certain cystidians and a few true crinoids, the 



