636 Dr. F. A. Bather — Notes on Yunnan Cystidea. 



(Text-fig. 11). Resting on the rebate is a series of squarish plates, 

 with their upper angles irregularly bevelled off. On the larger 

 shoulder of each such plate rests a triangular plate; in side view 

 this does not appear triangular because its apex is bent over on to 

 the other side (as seen in I, 2). The apices of the corresponding 

 triangular plates of the other side, similarly bent over, are seen 

 resting on the smaller shoulders of the squarish plates. There are 

 slight deviations from this general structure, but the essential fact 

 to notice is that the triangular plates cross the median line and 

 interlock. The appearance forcibly suggests that the cover-plates 

 did not open but formed a fixed tegmen. In any case a slit which, 

 as in I, 4, cuts across the triangular plates, cannot represent a 

 natural opening. 



The Hydropore has been mentioned in connexion with the 

 orientation of the subvective system. It is always concave towards 

 the peristome and tends to face its left corner (the supposed primitive 

 oral pole). In I, 4 the slit seems to branch at its riglit end, but 

 probably there is a small root of another cystid growing across it 

 (omitted in Text-fig. 9). 



The following are some measurements in millimetres of the 

 hexagonal Anal pyramid : — 



Specimen . . 1 2 3 4 5 



Least distance of anal centre from 



edge of peristome 

 Diameter, side to side . 



, , angle to angle 

 Length of peristome, circa . 

 The approximate length of 



comparison witli Dr. Reed's statement that the anus is " distant from 

 it [the 'mouth'] about twice its [the 'mouth's'] length". According 

 to the fixed points selected for the above measurements, this ratio of 

 2 : 1 holds for specimens 3 and 4 ; the ratio for I, 1 is 4 : 1 ; for 

 I, 2, 3:1; and for I, 5, 1"6 : 1. Arranging the specimens in order 

 of size, downwards, the ratios are 2, 3, 4, 2, 1"6. The chief interest 

 lies in the irregularity and lack of any correspondence between size 

 and position, which indicate that the anus did not migrate appreciably 

 during growth {v. supra, p. 534). 



The Gouopore is siibcircular with a tendency to be pentagonal, this 

 outline suggesting that the opening wa's closed by five valves, though 

 no other traces of them are preserved. 



The following measurements in millimetres show that irregularity 

 also obtains in the distance of this from tlie anus : — 



Specimen. . . 1 2 3 4 5 



Distance of Gonopore centre from 



anal centre .... 9-2 6-0 3-7 4-3 3-7 



Diameter of Gonopore lumen, circa — 1-4 1-3 -6 — 



The edge of the gonopore is raised slightly in I, 3, 5, and conspicuously 

 in 4 ; in I, 2 the rim is very faint, and in I, 1 not distinguishable. 

 In I, 4 and 5 the line joining the anal and gonopore centres is 

 parallel to the peristome ; but in I, 2 and 3 the gonopore is slightly 

 nearer the peristome. It is always to the left of the anal plane 

 (cf. Text-fig. 8). 



