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



being made up of a new dorsal portion intimately associated with 

 the eye, and an anterior portion which is probably a section of the 

 marginal suture. The posterior section of the latter seems to have 

 been completely replaced functionally by the newly instituted line 

 running behind the visual area. The whole of the*marginal suture 

 was liable to be resuscitated in forms which, like Trinucleus, became 

 blind secondarily and thus had no special use for a dorsal suture. 



The position of the marginal suture, whether primarily or 

 secondarily instituted, lay somewhere in the vicinity of the margin 

 of the cephalon. For the present it may be left as an unsettled 

 point whether the suture seen near the margin in such blind forms 

 as Conocoryphe and Ampyx is a true facial suture or a marginal one. 

 The line of reasoning followed above points to the latter as the 

 correct interpretation. 



The theoretic implications of the name Hypoparia render it 

 unsuitable for describing those forms in which a dorsal suture has 

 not yet appeared, and in which the marginal suture is of primary 

 origin ; hence the introduction of the name Protoparia for these. 

 The Protoparia cannot include Trinucleus, for that is a highly 

 specialized, not degenerate Opisthoparian, neither can it include 

 Agnostus, for that is an even more highly specialized Proparian. 

 This being the case Eaymond's suggestion that the terms Hypoparia 

 and Protoparia are practically synonymous cannot be accepted. 1 



III. — Notes on Yunnan Cystidea. III. Sinocystis compared with 



similar Genera. 



By F. A. Bather, D.Sc, F.E.S. 



(Published by permission of the Trustees of the British Museum.) 



(PLATE III.) 



P». — Comparison with Megacystis (continued). 



3. Structure of the Pores in Megacystis. 



ESSENTIALLY the pores of Megacystis are diplopores, for they 

 are arranged in pairs. This is evident on the inner surface of 

 a plate (E 16169, E 7671). Here each pore-pair lies in a shallow 

 depression, and each pore again lies in a slight depression at the 

 bottom of this (fig. 14). Compare Sinocystis yunnatiensis (antea, 

 p. 538). 



From these inner openings the pore-canals pass outwards through 

 the meso-stereom, still retaining their paired character. This can be 

 traced in vertical sections, since the canals as a rule follow a fairly 

 straight course normal to the surfaces ; but it is more easily seen in 

 horizontal sections of a plate (E 7675), or in the naturally worn 

 surfaces. For instance, E 16169 shows the co-channels in only a 

 small region, while the remaining surface is worn, with the result 

 that the structures manifest all over the theca appear to be ordinary 

 diplopores. This effect is particularly obvious when the pore-canals 

 have been filled with a dark matrix" (e.g. E 7644, E 7641). Some- 

 times the matrix has been dissolved out, leaving the canals empty 

 (E 16171). 



1 1916, p. 209. 



