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



There is yet a third hypothesis. By placing his Trematocystis 

 with Aristocystis in a family Aristocystidae, Dr. Jaekel implies that 

 the channel-systems were derived from the irregular groves of the 

 latter genus. He says in effect : — In this family of Diploporita the 

 peripores are lengthened in worm-fashion and form closed respiratory 

 spaces beneath the epistereom. In Aristocystis the epistereom shows 

 a smooth surface, and the pores are not visible till this is removed. 

 They are then seen to be connected by irregular channels — the 

 elongate peripores — and each channel may include two or more 

 pores. One of Jaekel's drawings (p. 409) shows as many as four 

 pores, three at the ends of a Y and one at the fork. One of 

 Barrande's figures (1887, pi. 38, fig. 23) shows six pores in a 

 channel. In Trematocystis, Jaekel continues, this tubular elongation 

 of the peripores led to their duplication and combination, while the 

 mesostereom also shared in their envelopment. 



It is not quite easy to follow this account. In the first place there 

 is still room for scepticism concerning the covering of epistereom. 

 The outer layer seen in many of these Bohemian fossils has not yet 

 manifested any structure, and may be nothing more than an 

 adherent film of limonite induced by the decay of the organic stroma. 

 Secondly, the account implies that the channel-systems of 

 Trematocystis, or at any rate the more complicated ones, involve 

 more than two pores; as already stated, I am unable to confirm this. 

 Thirdly, the interposition of the peculiarly irregular stage repre- 

 sented by Aristocystis bohemicus between the normal diplopore and 

 the simplest system seen in Trematocystis raises a gratuitous difficulty, 

 and one apparently inconsistent with Jaekel's own comparison of the 

 two latter. 



Possibly Jaekel had in mind (though he did not mention them) the 

 channel-systems of Hippocystis {antea, p. 72). There is an obvious 

 resemblance between an omega and two horseshoes set side by side 

 with the adjacent ends meeting in a single pore. But closer scrutiny 

 of the facts renders it doubtful whether a system of this pattern is 

 ever found in either Megacystis or Hippocystis: in the former, if the 

 pattern resembles an omega, it is with a difference, and there are two 

 pores to the system, not three ; in the latter the horseshoes neither 

 meet nor overlap, so far as one can judge from Barrande's figures and 

 description. It is therefore no easier to derive the Megacystis system 

 from that of Hippocystis than from any simple diplopore. 



On the whole the second of the three hypotheses here discussed 

 seems best to harmonize the various views that have been expressed 

 as well as the greater number of the structural facts. The idea that 

 the assumed papulae tend to be calcified is confirmed by the lofty 

 pore-pustules of Sinocystis loczyi and the pore - turrets of 

 8. yunnanensis. The supposed clogging by excess of calcification is 

 confirmed by the pepper-box pustules of Caryocrinus ornatus. Two 

 large tubercles of similar nature appear, as a result of individual and 

 local hypertrophy, in the holotype of Megacystis hammelli (Miller, 

 sub Holoci/ stif.es). Whether the elongation and sinuosity of the 

 peripores in Aristocystis was due to a similar need for extending the 

 respiratory surface, cannot be decided. At anv rate the channel- 



