IN THE MORPHOLO&T OP THE CTSTIDEA. 11 



White * has described a Devonian genus, Strohilocystis, in whicli 

 " the principal plates are probably similar to those of Gallocystis.'''' 

 It has three pairs of rbombs, but only four ambulacra. Its 

 generic position must, therefore, remain uncertain till the com- 

 position of its calyx can be definitely ascertained. 



"We have seen that in the bifasciate Pseudocrinus the inter- 

 radial AB is undeveloped, while in Apiocystis that of CD is perhaps 

 wanting. Cystoilasttis is distinguished by the absence of any 

 plate in interradius DE, the suture between these radials being 

 continued right up to the peristome, just as in many Blastoids 

 (PL I. fig. 7). This type is farther remarkable for the entry of 

 th.e other four interradials into the radial ring, two of them (17, 

 18) appearing in the figure. In fact, No. 18 forms the right-hand 

 margin of the anal aperture, and cuts plate 14 off from it 

 altogether. It may be noted too that in Gystohlastus, as in the 

 Russian species of EcMnoencrinus (PI. I. fig. 4), there is a pore- 

 rhomb on plates 1-6 in addition to that on 1-5, as Volborth t and 

 Schmidt % have already pointed out. 



Another remarkable form with the same two basal rhombs and 

 largely developed interradials (?) is the G-lyptocystis multipora 

 of Billings § (PI. I. fig. 8). Plates 16 and 17 are both of unusual 

 size, the former coming down to rest on basal 5, so as to separate 

 radials 10 and 11, whicb last is a small plate, just as in Gallocystis 

 (fig. 5) ; while No. 12 is also much reduced, and plate 7 is alto- 

 gether to the left of the anus, whicb is bounded by basal 8 and 

 radials 13, 14, as it would be in Gystohlastus, but for the low 

 position of interradial 18 (PI. I. fig. 7). On the other hand, in 

 the Russian Glyptocystis pennigera, the anal opening is greatly 

 extended at the expense of two basals (7, 8) and three radials 

 (12, 13, 14), and was covered, according to Schmidt||, by a delicate 

 plated integument. From such a form as this the transition is 



* "Descriptious of New Fossils from Palaeozoic Eocks of Iowa," Proc. Acad. 

 Nat. Sci. Philad. 1876, p. 28. 



t Mem. Acad. Sci. St. Petersbourg, 1870, tome xvi. no. 2, p. 12. 



\ " Ueber einige neue mid wenig bekannte Baltisch-Silurische Petrefacten," 

 ibid. 1874, tome xxi. no. 11, p. 10. 



§ " On the Cystidege of the Lower Sikiriau Eocks of Canada," Figures and 

 Descriptions of Canadian Organic Eemains, decade iii. 1858, p. 54, pi. iii. 



II Loc. cit. p. 18, tab. i. figs. 7 d, 10. [N.B. — Schmidt's numbering goes from 

 right to left across the page ; while that of Forbes, which I have followed, goes 

 from left to right. If Schmidt's figures be altered in accordance with this plan, 

 basal 9, beneath the anus, becomes basal 7, as I have implied above.] 



