622 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



his father, an isopod of the genus Anilocra with similar habits, an undetermined 

 crustacean sometimes found encysted in the disk of Heliometra glacialis, and an 

 internal worm wliich he discovered in Comanthus parvicirra. 



Regarding external parasites and commensals he cites the myzostomes, and 

 gives ophiurans, aphroditaceans, amphipods (which he erroneously regards as 

 the same as the isopod found by himself), and alpheids on the authority of von 

 Willemoes-Suhm. 



He further states that he has frequently found ophiurans entangled in the cirri, 

 which he regards are probably accidental, and once an ophiuroid pluteus attached 

 to a stem fi-agment of Metacrinus, while small bivalves, sertularian hydroids, 

 bryozoans, tubicolous annelids, and corals may be attached to the column of the 

 stalked types, not for any special nutritive purpose, but simply because the larvse 

 had to find a resting place somewhere. Various species of cirripeds are also fre- 

 quently met with on the stems and cirri of the pentacrinites. 



He mentions Stylina on Antedon viediterranea, and says that Rhizocnrms 

 lofotensis is often similarly infested Avith two or three small shells of StUifer, 

 which bore comparatively large holes in its calyx. He notes Truncatulina lobatula 

 as abundant on the cirri of certain arctic comatulids which he examined, and Poly- 

 trema miniaceum as common on the columns and cirri of certain pentacrinites 

 dredged by the Challenger in the East Indian region. 



Alcock in 1902 wrote: 



I have already mentioned the sea lily, striped in alternate bands of yellow and purple, on 

 whose fronds similarly striped crustaceans live without fear of detection; here we found the 

 same sea Illy giving secure shelter to sea worms, banded yellow and purple like Itself. 



In 1904 Mr. H. C. Chadwick stated that a specimen of Comanthus parvicirra 

 from the Gulf of Manaar, Ceylon, which when living was a deep olive brown 

 with the tips of the pinnules yellow, had living upon it an alpheid which was olive 

 brown striped with gray; and in 1908 he recorded a predominantly yellow speci- 

 men of Lamprometra palmata from Suez which had a brown commensal polynoid 

 living upon it, and an example of Heterometra savig^iii from Ul Shubuk which 

 when living was whitish with a violet tinge and with patches of darker color and 

 of yellow, from which were taken 15 ophiurans which lived with their arms 

 twisted around those of the crinoid, and of whicli the color on the whole resembled 

 that of their host. 



In 1915 Lieut. F. A. Potts, who had made a special study of the commensalism 

 between comatulids and other organisms at Torres Strait, published a most in- 

 teresting memoir on the subject, in which he went into considerable detail regard- 

 ing the color relations between the hosts and the commensals, and brought out 

 many new facts bearing on their ecological interrelationships. In this paper he 

 described as commensals on comatulids a new genus of amphipods, a new isopod, 

 two new galatheids, a new Synalpheus, and a new Polyno'e, and published detailed 

 notes on the three species of commensal Pontoniidse discovered by him and recently 

 described by Borradaile. 



