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THE AMEBIC AN NATURALIST [Vol. XLIII 



numerous known Silurian species of crinoids, starfishes, 

 opliiurans and echinoids were regularly five-rayed. 

 From the Devonian, several genera of starfishes with 

 multiple rays are known. They have the aspect of Cross- 

 aster, Labidiaster and Cronaster. But their real affini- 

 ties are doubtful. Those found in the Mesozoic and Ter- 

 tiary times, with rare exceptions, are five-rayed. 



At the present time all echinoids and holothurians are 

 normally five-rayed. Instances of monstrous specimens 

 with four rays or six rays are very rare in these large and 

 universally distributed groups. 12 



The modern crinoids only rarely depart from the 

 five-rayed condition, even as monstrosities. The ophiu- 

 rans show more variation in this respect. The common 

 genus Ophiactis, varies, when young, from six-rayed to 

 eight-rayed in nearly all of its species. But such species 

 are usually autotomous, and when adult become regularly 

 either five-rayed or six-rayed. 



Ophiocoma pumila, at Bermuda, is about as often regu- 

 larly six-rayed as five-rayed. Ophioglypha hexactis of 

 Kerguelen Island is regularly six-rayed. 



I have observed a large, regular, four-rayed example of 

 Ophiomnsiitm Lymani from deep water off the New Kng- 

 land coast, but it was selected from thousands of five- 

 rayed ones. Other radial variations in ophiurans are 

 known to me, but they are not common, although the 

 species are very numerous and many are often taken in 

 vast numbers. 



Among living starfishes radial variations are far more 



"In the Museum of Yale University there is a full grown, regularly 



Philippi (Arch, fur Naturg., 1837, III, p. 241, pi. v) described a 



