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



all this tract forms a gentle eminence. In E 7677, there is a similar 

 sharp, but less regular, curve to the left at the aboral end of the 

 suture, and the rest of the suture is waved ; there is no obvious 

 eminence. In E 7637 there are three sharp curves to the left and 

 three to the right, beginning with a small one at the aboral end on 

 the left and increasing in swing towards the oral end; although 

 there is no trace of a pore or of an eminence, it cannot be doubted 

 that this exaggerated sinuosity does in some way represent the 

 foldings of the hydropore. 



The variations here described bear little or no relation to 

 differences that might be taken as specific. They show how easily 

 one may overlook the indication of a hydropore, especially when it 

 is merely a passage between two plates; and they warrant the 

 conclusion that a hydropore is present in all species of Megacystis, 

 though previously recorded only in 21. commoda, 21. gyrinus, and 

 M. hammelli. 



The Gronopore appears in one of two distinct places. In eleven 

 specimens out of the eighteen in which it is visible it pierces the 

 posterior Ad. II {antea, figs. 24, 26). It may be near the centre 

 or in either the adoral or aboral half of the plate, but always lies 

 to the left of the median line (E 7631,— 32,— 35,— 36,— 38^— 41, . 

 —44, — 73, — 74,-75). In E 7639, where there are abnormally two 

 posterior Ad. II, the gonopore is on the left-hand one. In the 

 remaining seven specimens the gonopore is on the right slope of 

 the left posterior facet-boss, sometimes very close to the brachial 

 facet itself, e.g. -7 mm. distant in E 7634, E 7640, -6 mm. in 

 E 16168, -5 mm. in E 7630, -4 mm. in E 7677, and -3 mm. in 

 E 7633 [antea, fig. 22). This position is more than a mere crossing 

 over the suture between the facet-bearing plate and the interradial. 

 Only in E 7642 is the opening as near to that suture as it is to the 

 facet, the respective distances being each 1*3 mm. ; in this particular 

 case the left posterior facet is curiously widened in the direction 

 of the gonopore, as though stretching out to meet it. Remembering 

 that in the Crinoidea the genital strand passes into the arms, some 

 may see here the beginning of a similar relation. The brachia of 

 a crinoid, however, are outgrowths of the theca and contain 

 extensions of the body-cavity; in this they differ fundamentally 

 from the brachioles of a cystid, which are purely epithecal 

 structures, and contain, so far as one can see, no such extensions. 

 Carpenter (1891, p. 49) drew attention to a somewhat similar 

 variation in two of Barrande's examples of Aristocystis bohemica : 

 "In one of them the distal opening, which I regard as genital, 

 is on the very edge of the anal aperture, while in the other it is 

 nearly halfway up towards the peristome"; it remains, however, 

 on a plate distinct from that connected with the brachiole. 



From Miller's descriptions or figures it is inferred that the 

 gonopore is on the posterior Adoral II in nine species, viz., 21. 

 baculus, commoda, faberi, hammelli, ornata, parvula, rotunda, scitulus, 

 and splendens [antea, figs. 23, 28) ; near the left posterior facet in 

 four species, viz., 2£. gyrinus (fig. 30), plena, pustulosa, and 

 subglobosa. It has not been recognized in any other of the described 



