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



to the anal plane. Removal of the infilling matrix shows that the 

 quadrangular outline is furnished by a slight ridge which bounds 

 the peristome and joins up the four brachiole-facets that lie one at 

 each angle. The ridge on each side is frequently a little curved, 

 with an adoral convexity, and it does not meet adjacent ridges, but 

 merges into the margin of each brachiole-facet. Within this rim the 

 surface slopes downwards to an elliptical margin, and thence passes 

 vertically downwards as a tube of uncertain depth. 



Just within the quadrangular rim the slope is generally indented 

 by a slight rebate, and along this the inner side of the ridge is 

 marked by a row of notches, irregular in shape and size, but 

 generally appearing as vertical indentations with a rounded upper 

 end. These no doubt bore a series of small plates that covered the 

 peristome and subvective grooves, as in Sinocystis. The alternative 

 suggestion that there were large tegminals, each attached by a toothed 

 hinge, is opposed to the fact that no such plates have ever been 

 found. 



From the elliptical margin a narrow groove leads to each 

 brachiole-facet, whence no doubt it continued on to the brachiole 

 itself, as a subvective groove. E"o remains of brachioles have yet 

 been recognized. 



The thecal plates forming the margin of the peristome are six in 

 number; of these there are two on the anterior margin, two on 

 the posterior, and one at each side. The four subvective grooves lie 

 on the sutures between these last and the adjacent plates. All these 

 form Adoral circlet I, and may be called Adorals I (Ad. I). 



Outside them comes Adoral circlet II, composed of eight plates 

 (Adorals II, or Ad. II), namely, one supporting each brachiole- 

 facet, and therefore corresponding with the sutures at the angles of 

 the peristome, and four lying between these. The former four might 

 be designated ' radials ', and the latter four ' interradials '. Of the 

 interradials, the two on each side butt on the right and left adorals of 

 circlet I ; the two that are anterior and posterior alternate with the 

 paired anterior and posterior Adorals I, i.e. correspond with the 

 anterior and posterior sutures. 



This arrangement is shown in only two of Miller's figures, namely 

 those of " Holocystites " commodus (our fig. 23) and H. gorbyi, which 

 are probably synonymous. The figures of H. parvus and H. scitulus 

 show the eight Adorals II, but in Adorals I the two posterior plates 

 are not distinguished, and in the anterior interradius only one plate 

 is drawn. Probably the structure was quite normal, though the two 

 anterior Adorals I may conceivably have fused. 



The peristome of H. ornatus was described by Miller (1878) as 

 "surrounded by seven plates, and four (possibly five) arm bases". 

 The figure, when interpreted by our present knowledge, shows that 

 the Adorals I have been either not preserved or not distinguished, 

 except in the case of the two posterior. Assuming the facets to be, 

 as usual, on Adorals II, then there are, as usual, eight plates in that 

 circlet. The specimen therefore is probably of the normal (Ad. I, 6 ; 

 Ad. II, 8) type ; no reason is given for supposing that it had more 

 than four facets. 



