438 Mr. W. G. Eidcwood on 



tlien appear as an external flange set at some distance below 

 the ujiper end of the tube. 



The other specimen figured (PI. XII., A) measures about 

 28 x4-tx 30 mm. None of the tubes are more than 20 mm. 

 in lengthj and tiie ostia are almost ail transverse, like those 

 shown in the text-fig., a. 



The zooids agree in size with those of Cephihiliacna densus 

 descrilied in the 'Terra Nova' report (i6). In the table 

 below, the first numeral re[)resent3 the length in millimetres 

 from the tips o£ the arms to the c^ecal end of the body — that 

 is to say, the total length of the body, not counting the stalk; 

 the second stands for the length from the bases of the arms — 

 I. e., the anal region of the bod}' — to thecsecal end ; the third 

 is the average -width of the body. The constancy in the third 

 measurement is evidently associated with the uniformity in 

 the internal diameter of the coenoecial tubes from which the 

 zooids were extracted : — 



5-8 3-4 0-9 5-2 3-0 0-9 



.5-7 4-1 0-9 4-8 3-0 09 



5-6 40 0-9 4-6 3-0 0-1) 



There is no reason to suppose that anything but alcohol 

 was employed f')r tiie preservation of the material, and con- 

 sidering that, excefit for an occasional inspection, the specimens 

 have been untouched for nearly fifty years, the condition of 

 the zooids is remarkably good. For general purposes alcohol 

 still remains one of our most satisfactory preservative fluids ; 

 in the ' Terra Nova ' material of Cephahdiscus densus it was 

 noted that the zooids were in a better state of fixation in the 

 alcohol-preserved material than in that preserved in formalin 

 solution (i6^ p. 47). 



In colour the zooids are ochreous, but if removed from the 

 tubes and kept in alcohol in the light they become darker 

 and assume a greenish-broAvn tint. Four selected zooids were 

 '•ut into serial sections, but they present no new features. 

 Tiie notochord measures from 0*24 to 0*29 mm. in length and 

 from 0*02 to 0*03 mm. in sagittal diameter; the cavity of 

 the basal part is discontinuous, there being four or five 

 irregular partitions. 



Tlie arms are in most cases sixteen, but t.vo zooids were 

 found to have seventeen, two eigiiteen, and one nineteen. In 

 two of the zooids examined one of tiie marginal arms, next 

 to the edge of tiie oral lamella, was a diminutive, arrested 

 arm with not more than ten or twelve pairs of tentacles 

 {cf. i6, p. 45, text-fig. 6, h). The tentacles in a fully- 

 developed arm consist of forty to fift}' pairs. 



In the tubes of tlie iiiece of colony shown in PI. XII., B, 

 there occur tliree kind 4 of zooids — tiiose with two ovaries, 



