6o 



THE CYSTJDEA 



Cystoblastus) ; the extension of the subvective system over the thecal 

 plates, by the proliferation from plates 20-24 of alternating series 

 of plates, in which every other plate bears a brachiole (Schizocysti*, 

 Glyptocystis, Lepadocystis, Callocystis, Sphaerocystis, Lepadocrinus, Pseudo- 

 crinus) ; the atrophy of the anterior groove (partially in Glyptocystis, more 

 so in Prunocystis and Schizocystis, wholly in Lepadocrinus, Sphaerocystis, 

 and Strobilocystis) ; atrophy of two side grooves in addition (Schizocystis, 

 Pseudocrinus, Pleurocystis) ; restriction of pectinirhombs to sutures 

 between 1 & 5, 14 & 15, and 12 & 18 (Prunocystis, Schizocystis, Pseudo- 

 crinus, Lepadocrinus, Callocystis). None of these characters can be taken 

 as a basis of classification ; each group so formed would include genera 

 very diverse in other respects ; doubtless the same structures have in 

 many cases been independently attained. Happily certain relationships 

 seern clear, and round them the genera may be gathered into sub-families. 

 SUB- FAMILY 1, ECHINOENCRININAE, passes from the simple form 



FIG. XXII. 



Echinoencriniis Sencken- 

 bergi, after Jaekel. 



Fio. XXIII. 



Analysis of Echinocncrinus, original, after 

 specimen E12C5 in Brit. Mus. 



Fin. XXIV. 



Prunocystis Fletcheri (fronr. 

 Brit. Mus., 40207). Sh, 

 pectinirhorab. x 4 cliam. 



Echinoencrinus, in the direction of extension of two of the lateral grooves 

 over the theca, through Prunocystis to Schizocystis ; pectinirhombs 1 & 5 and 

 14 & 15 always, 12 & 18 frequently present, but no others, except 1 & 6 

 in Echinoencrinus. Genera Echinoencrinus, H. v. Meyer (1826;synn. 

 Gonocrinus, Eichwald, 1840, and Sycocystis, von Buch, 1845 ; see also 

 Volborth, 1842), Ordovician, Russia, differs from the imagined archetype 

 in restriction of pectinirhombs to 1 & 5, 1 & 6, and 14 & 15, and 

 in apparent bisection of plate 23 (Fig. XXIIL). The main grooves 

 may support five brachioles, or only two, or may branch yet more ; in 

 any case the facets are always close around the mouth. Anal region often 

 prominent (Erinocystis, Jaekel, 1899). The plates usually have strong 

 radiating folds, often crossed by finer concentric ridges (Fig. XXII.). 

 Here Jaekel (1899) places his Glaphyrocystis and Scoliocystis, Ordovician, 

 Russia. Prunocystis, Forbes (1848), Silurian, England, includes P. 

 Fletcheri and Echinoencrinus baccatiw, Forbes (Fig. XXIV.). Theca 

 " shaped like the fruit of a dog-rose." Adoral row of plates increased 

 in number. Pectinirhombs on 1 & 5, 14 & 15, and 12 & 18 only. 



