Early paleozoic bryozoa of the Baltic provinces. 179 



ance of being merely oblique diaphragms. The use of the cysti- 

 phragms is not known, but it is possible that they represent modified 

 ovicells. 



The method of zoarial growth in the family varies from incrusting 

 through lamellate, massive, and ramose, to bifoliate, intertwining 

 fronds. It is noteworthy that the massive, free forms of Prasopora, 

 the bifoliate forms of Peronopora, and the delicate incrusting zoaria 

 of Atactoporella, all of which are very abundant in certain faunas of 

 the North American Ordovician, should be entirely absent in the 

 Russian deposits. 



Genus MONTICULIPORA D'Orbigny. 



MonticuUpora D'Orbigny, Prodr. de Pal., vol. 1, 1850, p. 25. — Milne-Edwards, 

 Hist. Nat. des Corall., vol. 3, 1860, p. 272. — Nicholson, Paleozoic Tabulate 

 Corals, 1879, p. 269; The Genus Monticulipora, 1881, p. 99. — Ulrich, Journ. 

 Cincinnati Soc. JSTat. Hist., vol. 5, 1882, pp. 153, 232.— Foord, Contr. Micro- 

 Pal. Cambro-Sil., 1883, p. 7.— Ulrich, Geol. Surv. Elinois, vol. 8, 1890, pp. 

 370, 407; Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 1893, p. 217; 

 Zittel's Textbook of Paleontology (Eng. ed.), 1896, p. 272.— Simpson, Four- 

 teenth Ann. Rep. State Geologist New York for the year 1894, 1897, p. 577. — 

 NiCKLEsand Bassler, Bull. 173, U. S. Geol. Surv., 1900, p. 28. — Ulrich and 

 Bassler, Smiths. Misc. Coll., vol. 47, 1904, p. 15. 



Peronopora (part) Nicholson, The Genus Monticulipora, 1881, p. 215. 



Originally this genus was the resting place for a most heterogeneous 

 lot of species, but to-day, through the work of Ulrich, its definite 

 characters, so clearly shown in thin sections, have been so well 

 indicated that there is no longer any excuse for erroneous generic 

 identification. The generic characters are, first, the occurrence of 

 cystiphragms in the zooecial tubes, both in the axial and peripheral 

 regions, and, second, the peculiarly granulose wall structure per- 

 taining to both zooecia and mesopores. This combination of char- 

 acters has been found in species ranging through all the various forms 

 of growth save the bifoliate. The mesopores also, when present, 

 are variable in number. The acanthopores are usually small and 

 numerous, but differ in their microscopic features from those of all 

 the other families of the Trepostomata, The structure of the acan- 

 thopores in Monticulipora is much like that of the granulose walls, 

 but the distinct central perforation and concentric rings of tissue 

 seen in so many forms are wanting entirely. 



Genotype. — Monticulipora mammulata D'Orbigny. Upper Ordo- 

 vician (Maysville) of the Ohio Basin. 



MONTICULIPORA ARBOREA BISPINULATA, new variety. 



Text fig. 93. 



Cfr. Monticulipora arborea Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 

 3, pt. 1, 1893, p. 220, pi. 20, figs. 1-9, 13, 14. 



Zoarium incrusting, both of the type-specimens forming thin 

 expansions less than 20 mm. in diameter upon brachiopods. Surface 



