EAEL.Y PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 267 



delicata Ulrich from the Hamilton group of Iowa and Illinois. Care- 

 ful comparison shows that the latter has distinctly smaller zooecia. 



Occurrence. — Rare in the Kegel limestone (D2) at Habbinem, 

 Esthonia. 



Holotype.—Csit. No. 57371, U.S.N.M. 



Family TREMATOPORID^ Ulrich. 



Zoaria incrusting, ramose or massive. Zooecial tubes thin and 

 irregular in the axial region, usually constricted where diaphragms are 

 inserted. Walls thickened in the mature region, with a distinct 

 divisional line where the zooecia are in contact. Acanthopores more 

 or less abundant; mesopores often abundant and of large size, their 

 apertures closed. 



Compared with the Halloporidse this family differs most obviously 

 in having closed mesopores and ''beaded" zooecial tubes caused b}^ the 

 constriction of the walls when a diaphragm is inserted. With the 

 emendation of the Halloporidse to include a species with a slight 

 development of acanthopores, the most noticeable distinction between 

 the t\yo families — the presence of the structures in one and not in the 

 other — is less marked although still of value. As a rule the Tremato- 

 porida^ have a general looseness and slight obscurity of structure 

 quite unlike that of any other family. For example, the walls are 

 not as clear and distinct as in the Amplexoporidse or Halloporidse, 

 the acanthopores have a less definite, clear cut structure, and the walls 

 are often undulating. It is difficult to describe this " trematoporoid " 

 structure, although it is usually recognized without difficulty after 

 one has learned it from experience. 



The specific and generic representation of the Trematoporidse is 



the largest of the Trepostomata. All of the American genera save 



one are represented, and, with further search, this exception, Stro- 



matotrypa, will probably also be found common to both continents. 



The unusually large specific development of Hemipliragma in European 



strata is an interesting feature brought out by the present studies, and 



indicates most decidedly the value of the semidiaphrams as a generic 



character. 



Genus TREMATOPORA Hall. 



Trematopora Hall, Amer. Journ. Sci., ser. 2, vol. 11, 1851, p. 400; Nat. Hist. 

 New York, Pal., vol. 2, 1852, p. 149.— Hall and Simpson, Nat. Hist. New 

 York, Pal. vol. 6, 1887, p. xiv.— Miller, North Amer. Geol. and Pal., 1889, 

 p. 328.— Ulrich, Geol. Surv. Illinois, vol. 8, 1890, pp. 373, 418; Geol. and 

 Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 1893, p. 308.— Simpson, Fourteenth 

 Ann. Rep. State Geologist of New York for the year 1894, 1897, p. 591.— 

 NiCKLES and Bassler, Bull. 173, U. S. Geol. Surv., 1900, p. 35.— Pocta, 

 Syst. Sil. du Centre Boheme, vol. 8, pt. 2, 1902, p. 314.— Bassler, Bull. 

 292, V. S. Geol. Surv., 1906, p. 43. 



Not Trematopora of Ulrich, 1882; Eichwald, 1860; Dybowski, 1877. 



At least 80 species of Paleozoic Bryozoa have been referred to 

 Trematopora, from time to time, but few of these are strictly con- 

 92602°— Bull. 77—11 19 



