100 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



Occurrence. — Kiickers shale (02), Baron Toll's estate, Esthonia. 

 Cotypes.—Q^ii. No. 57205, U.S.N.M. 



A thin section of one of the type-specimens is m the collection of the 

 British Museum. 



Genus FAVOSITELLA Etheridge and Foord. 



Favositella Etheridge and Foord, Ann. and Mag. Nat. Hist., ser. 5, vol. 13, 



1884, p. 472. 

 Bythotrypa Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 1893, p. 



324; Zittel's Textbook of Paleontology (Eng. ed.), 1896, p. 268.— Nickles 



and Bassler, Bull. 173, U. S. Geol. Sui-v., 1900, p. 24. 



Specimens of the type-species of the genus Favositella have recently 

 come into the possession of the National Museum, and, upon being 

 sectioned, have proved to belong to the same generic group well 

 described by Ulrich under the name of Bythotrypa. The figures by 

 Etheridge and Foord illustrating the internal structure are accurate 

 and sufficient for the identification of the species, but the title of 

 their article and their description of the genus, written evidently 

 with the supposed relationship of Favositella to Favosites in mind, are 

 so misleading that the identity of Bythotrypa and Favositella has 

 hitherto not been noted. With the two described species of Bytho- 

 trypa, several new American forms, the three species described in the 

 present paper, and the type-species of Favositella, as well as one or 

 two undescribed forms from the European Silurian, Favositella 

 attains a specific representation equal to that of many of the other 

 ceramoporoid genera. 



The authors of Favositella recognized distinct "mural pores of a 

 large size, remote and irregularly disposed" in their thin sections, 

 which caused them to consider the genus as related to Favosites. 

 They further state that ''in some specimens the mural pores have 

 been filled with chalcedony of a concentric structure. It may be 

 noted that the pores are so large as to be seen on a polished surface." 

 The specimens and thin sections used in my study of Favositella 

 interpuncta, the type-species, show these same pore-like structures, 

 but I am unable to recognize them as pores for the very simple reason 

 that in sections they appear, not in the zoo6cial tissue or penetrating 

 the walls, but isolated in the zooecial cavity. Thus, in a tangential 

 section, these "pores" may be seen as individual, round bodies in the 

 clay-filled zooecial cavity, or in the mesopores, with no relation to the 

 walls. From their position and composition it is evident that they 

 have nothing to do with the bryozoan itself, but are simply rounded, 

 siliceous bodies included in the other material filling the cell cavity. 

 The appearance of these included bodies in thin sections is shown at 

 c in figure 35. 



Curiously enough, mural pores do exist in this species, as is indicated 

 in the accompanying figures of a tangential and a vertical section. 



