Br. F. A. Bather— Notes on Yunnan Cystidea. 533 



The following are measurements in millimetres; 

 Specimen . 1 2 



Height . 74-7 71-0 



Greatest 44-5 40° 58-0 160° 

 diameters 43-8 160° 43-0 60° 



Diameters 11-0 13-9 ca. 8-5 15-0 7-3 10-7 9-0 



at base 9-0 10-4 10-3 6-3 8-1 •8-5 



Peristome 95° 106° 



plane 



Specimen 8 consists of two rather large but incomplete individuals in matrix. 

 In order to indicate the planes of compression, the oro-anal plane 



is marked 0°-180°, 0° being anterior, or North in the usual 



orientation of drawings of the adoral face. The angle formed by 



each plane of compression with the oro-anal plane is reckoned in 

 degrees on the right-hand side. The direction of the extended 

 peristome is denoted in the same way. From this it will be seen 

 that the compression bears n.o constant relation to any morphological 

 plane, and is tlierefore due to causes acting. after death. The theca 

 was essentially ovate-pyriform, and its true diameters may be 

 roughly estimated by taking the mean of the double measurements. 

 The theca was upi-ight (1, 3, 5 ?, and 6), or bent over on its stalk (2) 

 so as apparently to have almost lain oa the sea-floor; but since in 

 this case the anus would thus be facing the sea-floor, it is more 

 likely that tlie base was fixed to the side of some object. 



The variation of angle between the peristome plane and the anal 

 plane may be regarded as due either to a shifting obliquity of the 

 mouth or to the migration of the anus. If checked by reference to 

 the hydropore, it will be found that the former is probably the truer 

 statement. The bearing of this decision appears when one examines 

 the four branches, their direction and diverse lengths. It will then 

 be observed that the peristome is not an oblong, parallel to tlie 

 hydropore and at right angles to the anal plane, witli four equal 

 branches, passing one from each corner at equal angles. It is the 

 departures from that simple but imaginary scheme which are of real 

 interest, as pointing to the original plan of which the existing ones 

 are modifications (Text-fig. 8). The extreme of departure is provided 

 by I, 2, but similar features are seen, though less marked, in I, 1, 3, 

 and 4. First, as already shown by the table of measurements, the 

 peristome lies at an angle to the anal plane of 106°, or 16° in excess 

 of a right angle. Secondly, the hydropore slit, which is never qilite 

 straight, but concave towards the moutli in a more or less 

 symmetrical curve, is neitlier parallel to the peristome nor 

 symmetrically placed in regard to it; on the contrary a line joining 

 the centres of hydropore and anus wili, if produced, meet the 

 peristome at its left end, just where the branches diverge. Thirdly, 

 the brandies do not form equal angles with the peristome. The 

 two branches on the left include an angle rather greater than 90° 

 (actually 110° in specimen 2), and the peristome plane does not 

 bisect this angle but lies anterior to its bisection. On the right the 

 angle included by the branches is about 90°, and here the peristome 

 plane lies posterior to its bisection, and that in an even greater 

 degree. Fourthly, the branches are of diverse length; the left 



