184 



BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



Zoarium of lamellate, epithecated expansions composed of one 

 or more layers, each of which is usually several milhmeters in thick- 

 ness. Surface smooth, but exhibiting conspicuous clusters composed 

 of zooecia attaining a diameter one and one-half times as great as 

 that of the intermacular zooecia. Zooecia polygonal, thin walled, 

 four in 2 mm., counting from the center of a macula, or six of the 

 ordinary ones in the same space; when well preserved, showing minute 

 granulations along the walls and small acanthopores usually at the 

 angles. Mesopores wanting. Zooecial tubes thin walled in the short 

 axial region, slightly thickened in the peripheral, where they con- 

 tain a rather crowded series of curved diaphragms, three usually 

 occurring in the distance of a tube diameter. 



Occurrence. — Rare in the Lyckholm limestone (Fl), at Kertel, 



6 



d 



Fig. 96.— Oebigntella expansa baltica. a, tangential section, x20, passing theough a zone of cueved 

 diaphragms; 6, several zocecia of the same, X35; c, vertical section, XlO, theough an entiee 

 ZOARIAL layer; i, portion of the same section, X20. Lyckholm limestone (Fl), Kertel, island of 

 Dago. 



island of Dago. The species is not uncommon in the Niagaran 

 (Rochester) shale of New York and Canada. 



Holotype.—Csit. No. 57272, U.S.N.M. 



British Museum, thin section of the type-specimen. 



Genus HOMOTRYPA Ulrich. 



Homotrypa Ulrich, Joum. Cincinnati Soc. Nat. Hist., vol. 5, 1882, p. 240. — 

 FooRD, Contr. Micro-Pal. Cambro-Sil., 1883, p. 9. — Miller, North Amer. 

 Geol. and Pal., 1889, p. 309.— Ulrich, Geol. Siirv. Illinois, vol. 8, 1890, 

 pp. 370, 409; Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 1893, p. 235; 

 Zittel's Textbook of Paleontology (Eng. ed.), 1896, p. 273.— Simpson, 

 Fourteenth Ann. Rep. State Geologist New York for the year 1894, 1897, p. 

 575.— NicKLES and Bassler, Bull. 173, U. S. Geol. Surv., 1900, p. 29.— 

 Bassler, Proc. U. S. Nat. Mus., vol. 26, 1903, p. 565.— Cumings, Thirty- 

 second Ann. Rep. Dep. Geol. Nat. Res. Indiana, 1907, p. 748. 



