NORTH AMERICAN EARLY TERTIARY BRYOZOA. ' 639 



FIG. 198. Structure of the tubes and apertura. 



A. Transverse section, X 25, of Mccynoecia corniita, new species, a species with club-shaped 

 tubes. These appear smaller at the center. B. Transverse section, X 25, of IiJmoiica matjna, new 

 species, with the tubes smaller at the center of growth, here laterally placed. C. Longitudinal 

 thin section of Idinoin-a marmircrersa, new species, X 25, showing linear space separating tubes. 

 D. A branch of Entalopliora ccnomana D'Orbigny, enlarged, showing zone of growth. E. The 

 zone of growth and basal lamella of Plagioecia (Diastopora)latom(irginata, D'Orbigny. F. 

 Sketch showing relations of tentacular sheath and zooecial walls in a cyclostomatous bryozoan 

 (after Calvet, 1900) ; ox, zooecial orifice; d, diaphragmatic orifice: gt. subdiaphragmatic region 

 of the tentacular sheath ; gt', super diaphragmatic region of the tentacular sheath ; miipd, parie- 

 tal diaphragmatic muscles: /, tentacles. G. Surface of Plngioecia prolifera Busk, with orifices 

 closed by finely perforated lamella. H. Surface of Mesenteripora meandrina Busk. 1875, showing 

 lamella perforated at the middle. I. Plagioecia sarniensis Hincks. 1880, illustrating lamella sur- 

 mounted by a projecting tubule. (Figs. H-J after Busk.) J. Longitudinal thin section, X 12, of 

 Hornera concatenata Reuss showing deeply placed lamella. K. Section of Mecynoetia nigosa 

 Waters, 1S77, illustrating that the lamella is placed where the tube rises free from the zoarium. 

 L. Section of Ascosoecia Ititernlis D'Orbigny preserving a double lamella. (J-L after Waters.) 



