MV/OSTO.MIDA- llOI'LKN<iKK. 1:17 



chief difference being in tin- thickness of tin- <-vst-\v;ill, which is considerably less in the 

 Antarctic specimens than in those described liv v. Cratf. v. Stummer-Traunfels puts 

 forward the view that in the cvsticoloiis .M \ v.ostoinids the character of the cyst-wall is 

 likely to vary with different hosts, and also that large cysts may lie expected to possess 

 thinner walls than small ones; in this connection he calls attention to v. draff's state- 

 ment that the smallest of the tvpe cysts was of more solid consistency than the rest. 



Whilst T. Stummer-Traunfels 1 memoir was in preparation AlcClendon published a 

 second paper containing a short account of a still larger cyst of tin's species Irom the 

 Trinitv Islands: owing to its large size (7'5 mm. in length) and the uncalcified nature 

 of the cvst-wall lie considers it to represent a, new sub-species which he names 

 .I/, cysticolum cystihymenodes. 



The five cvsts obtained bv the " Terra Xova " Expedition are. with one exception, 

 larger than any previously recorded; they measure 6, 8. 10, 11 and I _' mm. in 

 length, respectively. Four of these cvsts were found attached to the bodv-discs of 

 Promachocrinus Tcerguelenensis, dredged at a depth of 547 metres at Station .">f)5 in the 

 McMurdo Sound, the fifth being fixed to a, fragment of a Crinoid arm* from Station 2'J4 

 in the Ross Sea at a depth of L'S!) metres. 



Except in si/e the latter specimen very closely resembles those described bv 

 v. Stummer-Traunfels. The cyst (Eig. ;">) is ovoid in shape, 10 mm. long, with a 

 maximum width of about ."> mm. ; it is attached by its whole length to the arm of 

 the Crinoid. along the ambulacra! groove. The cyst-wall is thin and flexible, and is 

 not calcified. 



The two openings at the extremities of the cyst are both quite conspicuous. 

 They are, however, very unequal in si/e ; the one directed towards the disc of the host 

 measures a, little less than a millimetre in diameter, whilst that at the opposite extremity 

 has a diameter of nearly ."> mm. The latter opening is not quite terminal, being set 

 slightly obliquely to the long axis of the cyst; through it the cloacal extremity of a 

 large ^lyxostome projects for about I '5 mm. 



As mentioned above, the tour cysts from Promachocrinus Tcerguelenensis are 

 peculiar in being attached to the body-discs of their hosts instead of to the arms: 

 three specimens of the Crinoid were found with the parasites, one bearing two cysts. 



The cysts have a characteristic and apparently constant position on the actinal 

 surfaces of the discs (Fig. (J). each has its anterior extremity in close proximitv to the 

 point of bifurcation of one of the posterior ambulacra! grooves, and is attached bv its 

 whole length along the branch of the groove which lies closest to the anal tube of the 

 Crinoid. In the case where I wo cysts occurred on the same host these occupied similar 

 positions on either side of the anal tube. 



The cysts from Promachocrinus kerguelenensis are approximately oval in shape. 



* The fragment can hardly In: determined with certainty, lint Prut'. F. J . Bell believes it to ha\c 

 belonged to Anti-dun mli-lnnt. S. F. H. 



