644 



BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



Dactylethrae. The dactylethrae are club-shaped tubes without polypide, with 

 the same diameter as the polypidian tubes; their orifice is polygonal and closed 

 by a calcareous lamella very finely perforated (fig. 205). They resemble the 

 tergopores in longitudinal sections but they differ in their calcareous closure. 

 Exteriorly the dactylethrae resemble cancelli but differ from them in longitudinal 



Fio. 206. Cancelli. 



A. Transverse thin sections, X 35, of two cancelli of TAchenopora holdsworthi Busk, 1875, 

 showing spinules of the interior. (After Waters, 1894.1 B. Tangential thin section of the dorsal, 

 X 25, of Liciicnopora grignoncmis Milne Edwards, 1S38. C. Longitudinal thin section, X 25, of 

 Lichenopora goldfussi Reuss, 1864. The cancelli are superposed and ramified. 



section, in their club-shaped cylindrical form, and in the absence of internal 

 spinules. They differ from the tergopores in their aspect which is oblique and not 

 at right angles, and in their calcareous closure. 



The physiological function of the dactylethrae is unknown. 



Cancelli. The cancelli have been interpreted in many different ways, 1 but fol- 

 lowing the principle of least change we have adopted the meaning held by the 

 zoologists. They are the cylindrical tubes closed by a finely perforated calcareous 

 lamella, which are garnished in the interior with numerous spinules. At the center 

 of the zoaria the cancelli are completely cylindrical: on the margins their lower 

 part is club-shaped (fig. 206). 



'For their history see Gregory, Catalogue Cretaceous Bryozoa, vol. 1. p. 12; vol. 3, p. xx. 



