Dr. F. A. Bather — Notes on Yunnan Gystidea. 257 



There are four other alleged species with four facets : 

 H. omatissimus (fig. 25), S. papulosus, H. subovatus, and II. asper. 

 These are all pustulate forms, and the first three differ only in the 

 number of thecal plates ; there are 6 rows with intercalated plates in 

 H. subovatus, 7 rows of unequally-sized plates in H. omatissimus, and 

 about 8 rows in H. papulosus. These differences, as we learn from 

 Sinocystis, are only those of growth. The names are therefore 

 synonymous and, since all were published at the same time (1891), 

 the name omatissimus, which comes first in the book, may be selected 

 for the species. H. asper seems to have more tumid plates, and the 

 periproct is elongate transversely, not diagonally as in the other 

 forms. It may perhaps be a distinct species. The four drawings of 

 the adoral surface agree so closely that they must be regarded as 

 correct, at least in so far as what they show (fig. 25). The peristome 

 has a thick rounded margin, and this probably represents Adorals I, 

 though the component plates are not distinguished in the figures and 

 indeed may have been fused. The outlines of Adorals II are 

 distinctly drawn and show only six plates, namely four with facets on 

 the right and left, one anterior, and one posterior. These two 

 interradial Ad. II are elongate, especially the posterior, which is 

 drawn as stretching from the elliptical periproct right up to the 

 peristomial rim. In this feature H. omatissimus and H. asper differ 

 from the normal plan represented by H. gorbyi (fig. 23), but a more 

 ■essential difference lies in the absence of the right and left inter- 

 radials from Adorals II. The specimen which R. It. Rowley (1903, 

 Greene's Contrib. Indiana Palaont., i, p. 166, pi. xlviii, figs. 16-18) 

 has referred doubtfully to II. papulosus probably does not belong to 

 this species, since it has adorals on the normal H. gorbyi plan. It 

 might be H. ornatus. There is in the British Museum no specimen 

 en the H. omatissimus plan. 



We may pause here to compare the arrangement of the adorals in 

 specimens with four facets with that in the earlier form Sinocystis, 

 which also has four facets (antea, fig. 9, 1918, p. 535). The four 

 facet-bearing plates in that genus are presumably homologous with 

 the facet-bearing Adorals II of Megacystis. They appear, however, 

 to form part of Adoral circlet I, and those on the right and left join 

 . each other as in the omatissimus plan. On the other hand, there are 

 two anterior and two posterior Adorals I, as in the normal gorbyi 

 plan. It is possible that the right and left Adorals I are present but 

 hidden by the cover-plates. In that case there would, as in 

 Megacystis, be six Adorals I, forming a peristomial ring. The facet- 

 bearing plates of Sinocystis would thus fall into place as part of 

 Adoral circlet II, and the right and left Adorals II would be 

 represented by the plates that alternate with them ; but the 

 remaining plates of circlet II are more irregular in size and position 

 than in most (perhaps all) specimens of Megacystis. 



The occurrence of five facets in Megacystis is clearly shown in 

 S. A. Miller's figures of five species, but the arrangement of the 

 adorals is not so clear. Applying to the figures the knowledge 

 gained from the specimens previously discussed, we note that 

 Adorals I (though doubtless present) are not represented for any of 



DECADE VI.— VOL. VI. — NO. VI. 17 



