3 4 NATURAL HISTORY BULLETIN. 



The former were very likely the real adults of O. mulleri, as 

 he supposed. Therefore I think it best to apply a new name 

 to the form above described. Whether it be a variety or the 

 adult of O. krcbsii, or a distinct species, can only be deter- 

 mined by a larger series of intermediate sizes. 



Ophiactis krebsii Liitken. 



Ophiactis krcbsii Liitken, Vid. Meddel., p. 12, 1856; Addit. ad Hist. 

 Oph., Pt. II, p. 126. Lyman, 111. Cat. I, p. Ill, figs. 10, 11. Verrill, 

 notes on Radiata, Trans. Conn. Acad., I, p. 341, 366, 1868. 



Ophiactis savignyi (pars) Lyman, Report Voy. Challeng-er, Zool. 

 Ophiuroidea, V, p. 115, 1882. 



Bahama Bank, 12 young. Common from Charleston. S. 

 C. and Florida Reefs to the Abrolhos Reefs and Rio de 

 Janeiro, Brazil. Bermuda (Coll. Goode). It lives in the in- 

 terstices of sponges and corals, often gregariously while 

 young. 



Mr. Lyman considered it identical with O. savignyi and O. 

 virescens, from the Indian and Pacific oceans respectively. 

 With this opinion I am not prepared to agree. 



O. dispar appears to me to be more nearly related to O. 

 krebsii than to O. mulleri. The former has, even when of 

 very small size, with six rays, two mouth papillae, instead of 

 one. Its ventral plates have also a thickened or raised mar- 

 gin as in O. dispar and the arm-spines are more unequal and 

 more numerous than in O. mulleri. It is possible, therefore, that 

 the ordinary specimens of O. krebsii are all very young and 

 that when they grow to full size they may become regularly 

 five-rayed, as do some other echinoderms that undergo spon- 

 taneous fission and have a variable number of arms while 

 young. In that case it might, perhaps, develop into a species 

 like O. dispar. 



Family, OPHIACANTHID^ Ver. 



Ophiacanthince (sub-family of AmphiuridcB) Ljungman, 

 1866; Liitken, 1869. 



