438 Mr. W. G. Riaewood on 



ilieii appear aa an external flange set at some distance below 

 the npper end of the tube. 



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

 28 X 44 X 30 mm. None of the tiiljes are more than 20 mm. 

 in length, and the ostia are almost all transverse, like those 

 shown in the text-fiL;-., a. 



'I'he zooids agree in size with those of CepJidlo'/iscxs densus 

 described in the 'Terra Nova^ report (i6). la the table 

 below, the first numeral represents the length in millimetres 

 from the tips of the arms to the ca3cal end of the body — that 

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

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

 i. e., the anal region of the body — to thec?ecal end ; the third 

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

 jneasurement is evidently associated with the uniformity in 

 the internal diameter of the coenoe^ial tubes from which the 

 zooids were extracted : — 



5-8 3-4 OP 5-2 3(1 0-9 



5-7 4-1 0-9 4-8 30 0-9 



5-6 40 0-9 4-0 3-0 0'9 



There is no reason to suppose that anything but alcohol 

 was employed for the preservation of the material, and con- 

 sidering that, except for an occasional inspection, the specimens 

 have been untouched for nearly fifty years, the condition of 

 the zooids is remarkably good. For general j)nrposes alcohol 

 still remains one of our most satisfactory preservative fluids ; 

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

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

 alcohol-preserved material than in tliat 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-brown tint. Four selected zooids were 

 cut into serial sections, but they present no new features. 

 The 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. 



The arms are in most cases sixteen, but two zooids were 

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

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

 to the edge of the 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 tully- 

 developed arm consist of forty to fifty pairs. 



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

 there occur three kind-; of zooids — those with two ovaries. 



