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BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



Fig. 15a— Family Flustridae Smitt, 1867 



L. Flustra securifrons Pallas, 1766. Longitudinal section through two zooecia, 

 X40. The muscle of the ovicellarian operculum (m ov) is seen in the angle 

 between this operculum and its inner membraneous continuation; dw, cryptocyst 

 process (after Levinsen, 1909). 



M. Flustra membranaceo-truncata Smitt, 1867. Structure of the ovicell (after 

 Levinsen, 1909) ; cr, cryptocyst; cm, covering membrane (ectocyst) ; op, operculum; 

 ov, ovicellarian operculum; v, vestibule. 



N, O. Flustra securifrons Pallas, 1766. N. The distal wall, X26. (After 

 Waters, 1896). O. The distal wall from the distal end of a zooecium with ovi- 

 cell. The ovicellarian muscle and the two cryptocyst processes (d w are seen 

 X40). 



P. Flustra carbasea Solander, 1786. A transverse section through a branch, 

 X40. 



Q-S. Flustra foliacea Linnaeus, 1758. Q. Lateral view of the two ovicells; 

 d w, distal wall, X40. R. Two zooecia after boiling in caustic potash. The 

 lateral walls' composition of small plates is seen, X40. S. View from the basal 

 surface, after boiling in potash. The distal wall with its septular plates is seen 

 and the composition of the basal wall in small plates. A very few striations 

 parallel to the distal lines cannot be seen in this figure, X40. 



T. Flustra securifrons Pallas, 1766. Some zooecia after boiling in potash, to 

 show the process of calcification of the basal wall, X33. 



U. Spiralaria denticulata Busk, 1852. A portion of the basal surface, to show 

 its composition of cell-like small plates (cell mosaic). (N-U. After Levinsen, 

 1909.) 



