468 



NEW YORK STATE MUSEUM 



etched specimens that the stronger reticulate layer is covered internally and 

 externally by delicate continuous membranes. 



The internal skeleton has become known by the investigations of Tull- 



-VI 



454 



452 ir 453 455 



Fig. 449 Retiolites geini tzian us var. v e n o s us (Hall)._ Copy of one of Hall's original figures showing 

 the zigzagged axis and the meshes. Fig. 450,451 Retiolites geinitzianus Barrande. Fig. 450 Sicular end of 

 an etched specimen; the thick periderm is omitted. Fig. ^ 5 1 Section of the same, showing as the preceding figure the 

 straight axis (v 1), the zigzagged axis (v 2) and the connecting crossbars. Copies from Holm Fig. 452, 453 Retio- 

 lites nassa Holm. Fig. 452 Portion of rhabdosome near distal extremity showing main strands only. Fig. .153 

 Diagrammatic section to show position of longitudinal ledges or strands and of " virgnla." Copies from Wiinan. Fig. 

 454, 455 S t omat ograp t us grandis Suess sp. Fig. 454 Reconstruction (after Holm) to show- form of thecae. 

 Fig- 455 Flattened specimen. Copies from Perner 



berg, Tdrnquist, Jaekel, Holm and Wiman. It has been shown by these 

 authors that both lateral sides contain solid axes (" virgulas"), one of which 



