NORTH AMERICAN EARLY TERTIARY BRYOZOA. 



351 



Occurrence. Upper Jacksonian (Ocala limestone) : Chipola River, east of 

 Marianna, Florida (very rare) ; Old Factory, H miles above Bainbridge, Georgia 

 (rare). 



Hole-type. Cut, No. 64055, U.S.N.M. 



Genus ARTHROPOMA Levinsen, 1909. 



1009. Arthropoma LEVINSEN, Morphological and Systematic Studies on the Cheilostomatoua 

 Bryozoa, p. 332. 



The ovicell is hyperstomial and always closed by the operculum. The frontal 

 is a tremocyst with scattered pores. The operculum bears a mobile, small tongue 

 in the middle of the straight, proximal border. The rimule of the aperture is 

 straight and rectangular. 



FIG. 105. Genus Arthropoma Leviusen, 1909. 



A, D. Arthropoma cecilii Audouin, 1826. A. Zooecia, X 30. (After Hincks, 1880.) 

 B. Avicularian zooeoia. (After Kirkpatrick.) C. Operculum with its mobile tongue, X 85. 

 (After Waters, 1904.) D. Operculum, X 120. (After Busk, 1884.) cs., connected part of the 

 coinpensatrix, which by foldings has assumed the longitudinally striated appearance. 



E. Arthropoma circinata MacGillivray, 1868. Operculum and mandible, X 120. (After 

 Busk, 1884.) 



F, G. Arthropoma pesanseris Smitt, 1879. Operculum and mandibles, X 85. (After 

 Waters, 1899.) 



Genotype. Arthropoma (Flustra) cecilii Savigny-Audouiii (1812) 1826. 



Range. Jacksonian-Eecent. 



The little mobile tongue of the operculum is attached to the compensatrix. 

 This is the only character which differentiates this genus from Phonicosia Jullien, 

 1888, and if this be judged insufficient, it will be necessary to reunite the two 

 genera under the latter name, which has the right of priority. 



The mobility of the little tongue is evidently intended to protect from rupture 

 the compensatrix, which is an extremely fragile organ. 



Kirkpatrick has discovered a zooecium transformed into an interzooecial avicu- 

 larium with special mandible. Such zooecia are not rare in other genera and we 

 have sometimes noted them on the fossil forms. 



