Dr. F. A. Batlier — Notes on Yunnan Gystidea. 509 



It is not necessary to enquire whether this scheme is used quite 

 consistently by Dr. Heed ; it is doubtful whether it could be. Nor 

 need one do more than point out that Dr. Reed strays no less from 

 general custom in his use of the terms 'pole', 'meridian', 'right' 

 and ' left '. 



Unfortunately Dr. E,eed believes himself to have been following 

 the chapters in the "Treatise on Zoology" as his 'authority', a 

 compliment which is so effective a criticism of their lucidity that it 

 is necessary to make their scheme plainer in so far as it applies to 

 Cystidea. 



A pole is a point at which an imaginary axis cuts the circum- 

 ference of the theca. 



The oral pole coincides with the centre of the pei'istome {vide 

 infra). 



istenQP 



'sagittal 

 ^ 'plane 



nnmitive \ 

 ' sag'iMal \ 

 nlane\ 



anterior 



— hR. L. 



anterior 



..nensVonie 

 hlane 



Jilane 



anal \ 

 jvlane. 

 nvsterlor 



Fig. 3. — A diagram of the adoral face of Sinocystis mansuyi, after Eeed, 1917, 

 pi. II, fig. 7 ; the orientation according to Eeed. x |. 



Fig. 4. — The same ; the orientation according to Bather. The evidence for 

 the " primitive sagittal plane " is given in the notes on S. loczyi (part II, 

 fig. 8). 



The apical pole coincides with the centre of the basal attachment, 

 or with the centre of the system of plates in that region. 



A specialized apical system of plates comparable with that of 

 Crinoidea and Echinoidea has rarely been attained in Cystidea. 



The vertical axis cuts the theca at the oral and apical poles. 



The region of the thecal surface surrounding the oral pole is the 

 adoral face. 



The region surrounding the apical pole is the adapical face. 



The thecal openings are normally four: the peristome, often 

 called the 'mouth ', but that organ, strictly speaking, lay within it 

 and may have occupied but a small part of the peristomial area; the 

 periproct, often called the 'anus', but that organ lay within it and 

 occupied only a part of the periproctal area; the hydropore, some- 

 times in the form of a ' madreporite ', usually lying close to the 



