MONOGRAPH OF THE EXISTING CRINOIDS. 643 



The large number of these ophiurans found on a single crinoid appears to indi- 

 cate that they could not have belonged to any species of Ophiomaza, which nor- 

 mally occur singly, one to each crinoid, and suggests that they represented a species 

 of Ophiactis. 



OPniOPIIOLIS MIRABILIS (DUNCAN). 



A specimen of this species was found coiled tightly about the stem, just under 

 the crown, of a specimen of Metacrinus acutus dredged by the Albatross in the 

 Eastern Sea, off Kagoshima Gulf, in 105 to 152 fathoms. 



Family OPHIOTRICHID^, 



Many, if not most, of the species in this family are more or less strictly com- 

 mensal in habit. Some, as certain species of OpJtiothriv, are normally associated 

 with various aborescent organisms, and occasionally are to be found upon the penta- 

 crinites, and more rarely upon the comatulids; others, as the species of Ophwmaza, 

 are rarely found elsewhere than upon the comatulids. 



OpnioaiAZA. 



Ophiomaza is the only genus of ophiurans which has been determined to be 

 normally commensal upon the comatulids. It lives, oral surface downward, upon 

 the disk of the larger species, with the arms wrapped around the dorsal side of 

 the crinoid. 



The curiously banded or blotched type of coloration usually found in this 

 genus recalls that of other organisms commensal with the comatulids, and is remi- 

 niscent of Siffsbeia lineata Liitken and Mortensen, which is also commensal, though 

 not upon crinoids. 



OPHIOMAZA CACAOTICA LYMAN. 

 PI. 52, fig. 1341. 



The commensal ophiuran noted by von Willemoes-Suhm on black and white 

 comatulids from the Arafura Sea was probably this species. 



I have found it on Capillaster sentosa from Singapore, and on Heterometra 

 reynaudii from the entrance to Palk Strait, Ceylon, in 6 to 8 fathoms. 



Potts states that at Torres Strait he found it commensal on ComantKus annu- 

 latus, and that in color it was a uniform black, very deep purple, or brown. One 

 small black specimen was found on a bright red Comatula purpurea. 



This ophiuran probably occurs on any comatulid of sufficient size to support 

 it, regardless of species. So far as I have seen there is rarely, if ever, more than 

 one on a single crinoid. 



Ophiomaza cacaotica ranges from Zanzibar to Suez and eastward to northern 

 Australia, the Philippine Islands, and the China Sea, but apparently is nowhere 

 abundant. It occurs from the low-tide mark down to nearly 40 fathoms. 



Most of the records for the species make no mention of its commensalism. 



