Dr. F. A. Bather — Notes on Yunnan Cystidea. 535 



Sj'stem is not quite clear and does not seem to be constant. Each 

 facet appears, as Dr. Heed says, to be "situated in the centre of 

 a slightly swollen ordinary thecal plate". The hydropore seems at 

 first glance to be on a single plate, adjoining the peristome and 

 hlling the posterior interradius. On the other side of the peristome, 

 in the opposite interradius, two plates are discernible in I, 4, and 

 perhaps in 2 and 3. The thecal plates adjacent to the hydropore- 

 plate suggest that it too is really compound, and this view is 

 supported by S. mayisuyi, II, 9 (see Heed's figure). It is usual for 

 a hydropore- slit of this shape to cross a suture. This would give 

 8 adoral plates, of which the right and left pairs would bear facets ; 

 the posterior pair would bear the liydropore, and the anterior pair 

 would bear nothing (Text-fig. 9). The occurrence in all species of 

 Sinocystis of diplopores on all these plates, right up to the facets, 

 grooves, etc., is noteworthy (Text-fig. 12). 



10 12 



y,— 



11 



13 



Fig. 9. — Sinocystis loczyi: diagram of the eight adoral plates. The broken 



- lines are restored by me ; all others are traced from Mr. Brock's 



drawing (Beed, 1917, pi. i, fig. 4). x f. 



,, 10. — Sinocystis loczyi : section across the peristomial ridge ; the exterior 



outline based on 1, 4 ; the interior imaginary. The summit notch 



is due to weathering, x f . 



,, 11. — Sinocystis loczyi: side-view of a part of the peristomial ridge in 



I, 4, to show how the cover-plates interlock, x f . 



,, 12. — Sinocystis mansuyi: section across a subvective groove as seen in 



II, 7. Note pore-canals of a diplopore on the right, x f . 

 ,, 13. — Sinocystis mansuyi: the hydropore in II, 2. x circa^. 



Dr. Tteed says of S. loczyi "mouth narrow, straight, slit-like, 

 slightly raised". It is not certain what he means by "mouth". 

 Apparently the sentence quoted refers, to the thread-like slit clearly 

 shown in pi. I, fig. 4 (cf. Text-figs. 9, 10). This, however, is 

 not a natural opening into the thecal cavity. The peristomial 

 fvperture is not actually visible in any of the figured specimens. 

 From the disposition of the cover-plates, however, supported by the 

 evidence of closely similar fossils from elsewhere, it may be inferred 

 that the peristome in I, 1 was an oblong, measuring about 4-5 mm. 

 by not more than 2 mm. The aperture and the grooves leading from 

 its corners to the brachiole-facets were, as Dr. Heed says, " covered 

 with a double row of small alternate polygonal plates set in a narrow 

 rebate around their edges [i.e. of mouth and branches] and forming 

 XI roof-like ridge." The arrangement of the cover-plates is shoAvn, 

 though not very clearly, in Heed, pi. I, fig. 2a. It may be better 

 understood from the annexed side-view of the terminal ridjje in I, 4 



