32 CALAMOCRINUS DIOMED.E. 



lire 11 of Plate X., showing the base of another covering plate, the articu- 

 lating sjDurs are very prominent laterally, and from the base of the covering 

 plate a broad fan-like projection of open mesh work juts out beyond the 

 general outline. The mode of formation of the secondary reticulation from 

 Figures 9 and 11 of Plate X. is shown in Figure 12 of the same plate. 



Carpenter in his Challenger Report speaks of the great variety in the 

 covering and side plates of Pentacrinus. In Pentacrinus naresianus the 

 covering plates and side plates are fused, and form a long plate. They 

 are differentiated again in P. Blakei. Carpenter also calls attention to the 

 fact that in Metacrinus the side plates and covering plates are generally 

 better differentiated than in Pentacrinus. In Hyocrinus there are no side 

 plates on the arms, yet they are well developed on the enlarged parts of the 

 pinnules containing the genital glands (Chall. Rep., Plate \ c, Fig. 10, sp). 



Wachsmuth and Springer have mentioned * the existence of a small row 

 of side pieces on each side of the two rows of robust covering pieces in 

 Megistocrinus nobilis, W. & S. 



Interradial Plates. 



With the exception of Hj^ocrinus, none of the Stalked Crinoids discovered 

 by the recent deep-sea dredging expeditions possessed large distinct peri- 

 somic plates between the peristome and the edge of the cup. The presence 

 of a heavy interradial plating in Calamocrinus, similar in all respects to that 

 of Apiocrinus and Millericrinus, is an important structural feature hitherto 

 unknown in any recent Stalked Crinoid. The figures of Plates II. to VI. 

 nearly all illustrate some structural point of this interradial plating. 



The perisomic plating consists of two kinds of plates. One set, arranged 

 in from seven to eight irregular rows, the lower row resting directly upon 

 the upper faces of the radials, is made up of thick, irregularly shaped, 

 generally hexagonal plates, closely joined together by their apposed edges 

 so as to form a stout arch between the lower part of adjacent arms. These 

 plates are imperforate and closely soldered to the edges of the arm joints, 

 which throw out small wing-like appendages closely intercalated with the 

 perisomic plates, and forming a solid, practically rigid calyx as far as the 

 fourth or fifth joint of the second pinnule (Plates II., III., Plate IV. Figs. 

 9-14, Plate V. Figs. 1, 2, 4, Plate VI. Fig. 5). 



• Geol. Survey of Illinois, Vol. VIII. p. 171, 1S90. 



