676 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Various hydroids of several different families occur frequently on the stems 

 and cirri of the pentacrinites (pi. 52, fig. 1342), and on the cirri of the comatulids. 

 On the pentacrinites they often form tufts of very considerable size. 



Most of the species are merely of fortuitous occurrence, but some are commensal 

 and one or two probably semiparasitic. 



There are the following specific records. 



Family CAMPANULARIID^. 



CALTCELLA SYRIXGA LINNJEU8. 



This species was found by Mortensen on the cirri of Hathrometra prolixa, from 

 northeastern Greenland. 



8TEGOPOMA FA8TIGATU3I ALDER. 



This form occurs on the cirri of Hathrometra prolixa. It was recorded by 

 Mortensen from northeastern Greenland. 



CUSPIDELLA, SP. 



An undetermined species of Cuspidella was found by Mortensen on the cirri 

 of Hathrometra prolixa, from northeastern Greenland. 



Family PERISIPHONIDvE. 



LAFOEA FKUTICOSA (SARS). 



Lafoea fruticosa was found on the cirri of Hathrometra prolixa from north- 

 eastern Greenland by Mortensen. 



CORALS. 



P. H. Carpenter stated that corals may be attached to the columns of the 

 stalked crinoids. Probably he referred to the white form of Polytrema miniaceum, 

 which is quite coral-like in appearance. 



As would be expected, small colonies of hydrocorallines are sometimes found 

 on the older portions of the columns and on the accompanying cirri in the penta- 

 crinites, and, rarely, on the older cirri of the comatulids. 



It is rather curious that none of the Actiniaria or sea anemonies have as yet 

 been found upon the crinoids, as certain genera, such as Stephanactis, Amphianthus, 

 and Gephyra, occur very commonly on pennatulids and other arborescent marine 

 organisms. 



PORIFERA. 



Small sponges of various kinds are often found attached to the older portions 

 of the stems and to the cirri of the pentacrinites, and sometimes to the older cirri 

 of the comatulids. There is no evidence that their occurrence is other than 

 fortuitous. 



UNICELLULAR ORGANISMS. 



The unicellular organisms known to be commensal with, or parasitic upon or 

 within, the echinoderms, are fairly numerous, but only two genera have as yet been 



