456 



PELMATOZOA. 



the component halves of each are separated externally by an interval 

 (fig. 322, c). Of the more important genera of this group, Pleuro- 

 cystites is remarkable in having the perisomatic plates on the dorsal 

 side of the calyx large and definitely arranged, while those of the 

 ventral side are numerous and indefinite. The summit of the calyx 

 carries two jointed armlets (fig. 326, b), and there are three "pore- 

 rhombs," or, as these structures were termed by Edward Forbes, 

 " pectinated rhombs." The genus is found in the Ordovician rocks 

 of Canada. In the Ordovician genus Echinoencrinus (fig. 325, c) 

 the calyx is composed of four series of plates, there being four basals, 



Fig. 326. — a, Caryocrinus ornatus: a, Column; b, Calyx; c, Scars where pinnulae were 

 attached ; d, Valvular pyramid. B, Pleurocystites sguamosus (dorsal side) : p p, Two of the 

 pore-rhombs. c, Lepadocrinus (Pseudocrinus) bifasciatus. d, Lepadocrinus Gebkardi. 



and five plates in every cycle above this. There are. three "pectin- 

 ated rhombs," and the anal opening is of large size and is placed on 

 one side. The Silurian Cystideans referred to this genus by Edward 

 Forbes under the names of E. baccatus and E. armatus (fig. 325, d) 

 differ in some important points from the type of Echinoencrinus. 

 Glyptocystites, of the Ordovician rocks of America and Europe, is 

 allied to the preceding, but possesses numerous " pore-rhombs " (ten 

 to twelve in number), no other genus of this section having more 

 than three or four of these organs. In Lepadocrinus — with which 

 Zittel unites Pseudocrinus and Apiocystites — the calyx is ovoid, more 

 or less quadrangular, with a long stem, which becomes attenuated 



