62 



THE CYSTIDEA 



Pseudocrinus quadrifasciatus and P. oblongus), Silurian, North America, 

 England, Scandinavia (Fig. XXX.). Plates much as in Lepadocystis. 

 Pectinirhombs onl&5, 12&18, 14&15 only. Main grooves four, 

 the anterior being aborted, extend over theca to a degree that differs 

 in different species, and is always less in younger stages. Pseudocrinus, 



Pio. XXIX. 



Analysis of Pseudocrinus, based on specimens in 

 the British Museum, especially 40193. 



FIG. XXX. 



Restored Lepadocrinus quadrifasdatm. The arm- 

 lets of the outer rows are erect ; those of the middle 

 row depressed. Near the top of the left-hand quarter 

 is the anus ; near the top of the right-hand quarter 

 is a pectinirhon.b. By permission of the Keeper of 

 the Geological Dept. , British Museum. 



Pearce (1842, redescr. Forbes, 1848), Silurian, England (Fig. XXIX.). 

 Resembles a Lepadocrinus in which all main grooves are aborted except 

 apparently r. post, and 1. ant. The grooves are the same as those of 

 Sihizocystis, but their relation to the thecal plates and anus is as in 

 Lepadocrinus. The theca is compressed so as to have two almost flat 



oval sides, fringed by the 

 brachioles of these grooves ; 

 one side contains the anus 

 and pectinirhomb 14 & 15, 

 the other contains pectini- 

 rhombs 1 & 5, and 12 & 18. 

 Callocystis, Hall (1852, syn. 

 Anthocystis, Haeckel), Silurian, 

 North America (Fig. XXXI.). 

 Plates 10, 12, and 14 are 

 sunk down between 6 and 7, 

 8 an-1 9 respectively, so as to 

 rest on 2 and 3 ; thus there 

 appear to be eight plates in 

 the second circlet. Con trari wise, by the vertical elongation of 7 and 8, 

 13 is raised between 18 and 19. The remaining plate of the third 



<D 



FIG. XXXI. 

 Analysis of Callocystis Jewetti based on Hall's ligures. 



