24 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.61. 



antiqiia D'Orbigny, 1852 is synonymous with Splropora tetragoiia 

 Lamouroux, 1821. Finally Gregory in 1896 noted that the idmonei- 

 form arrangement of the apertures is not constant throughout the 

 whole zoarium. 



The consideration of the ovicell causes the classification of this 

 genus in the Mecynoeciidae. Examination of thin sections which 

 shows the very unexpected metopoporinan nature of the tubes, per- 

 mits us to maintain D'Orbigny's name but with a very different diag- 

 nosis. According to the section, Byirofora richraondensis Vine, 

 1884, belongs probably to this genus. We may here again note that 

 the exterior aspect and the arrangement of the tubes of the zoarium 

 can not furnish important characters for classification. For ex- 

 ample, Bisidmanea gabhiana Ulrich and Bassler, 1904, and b. 

 johristruppi Pergens and Meunier belongs to the Plagioeciidae, the 

 type species B. tetragona Lamouroux. 1821, to the Mecynoeciidae and 

 B. f glohuloecia^ new species to still another family. 



BISIDMONEA TETRAGONA Lamouroux, 1821. 



Plate 3, fig. 6. 



1821. Spiropora tetragonn Lamoitroxjx, Exposition metliodique, p. 85, pi. 82, 



figs. 9, 10. 

 1846. Cenopora tetragona Michemn. Iconographie zoophytolof^ique, p. 235, 



pi. 55, fig. 12. 



1852. Bisidm<niea antiqua d'Oimugny, Paleontologie francaise, Terraiu Cr^- 

 tace, p. 720, pi. 762, figs. 10-12. 



1896. Spiropora tetragona Gregory, Catalogue of tbe Jurassic Bryozoa in 

 tlie British Museum, p. 155, pi. 9, figs. 1 (Cites bibliograpliy and geo- 

 logical distribution). 



Structure. — The zoarial aspect is that of two specimens of Mffionea 

 joined by their dorsal but longitudinal sections show a very different 

 structure from typical Idmonea. The tubes are subcylindrical in a 

 part of their course, but they become very much expanded in their 

 terminal portion; their walls are vesicular and they are closed by a 

 facette (zooecial area) clearly limited exteriorily by salient threads. 

 We may mention again that the tubes with facettes, for which the 

 group Metopoporina was proposed, exist in almost all families of 

 Cyclostomata. 



Our specimens are small, and we have not been able to verify the 

 method of budding. As the transverse section shows at its center 

 very large tubes without interstitial tubes, peripheral gemmation is 

 not probable. The entire absence of the median lamella confirms the 

 fact that the zoarium is not formed of two Idmaneas joined by their 

 dorsal. The aperture is circular and placed entirely above the 

 zooecial area. The figure given by D'Orbigny is entirely too regular. 



