162 BULLETIN 77, UlvriTBD STATES NATIONAL MUSEUM. 



noncelluliferous and finely striated. Measuring longitudinally, four 

 zooecia occur in 2 mm. In cross-section, the zoarium is rounded 

 polygonal in outline, as shown in figure 81 e. The zooecia are about 

 their own length apart longitudinally and the several rows are 

 separated by a poorly developed ridge. 



The slender branches with one side noncelluliferous and striated, 

 and the rest of the surface celluliferous, are so distinct from all 

 associated bryozoans that comparisons are unnecessary. 



Occurrence. — Abundant in the Richmond division of the Anticosti 

 group on the island of Anticosti, where it is associated with equally 

 numerous specimens of Nematopora lineata. Apparently rare in the 

 Borkholm limestone (F2) at Borkholm, Esthonia (Cat. No. 57255, 

 U.S.N.M.), where also it occurs with Nematopora lineata. Also in 

 the Borkholm drift, Ojle Myr, island of Gothland, 



Family RHABDOMESONTIDiE Vine. 



Species of this family have hitherto not been recorded from strata 

 earlier than the Silurian, so that the occurrence of a new species of 

 RTiombopora, and at least one species of a new generic type in the 

 Middle Ordovician, is of considerable interest. The new genus is 

 peculiar in the development of a great number of mesopores, a fact 

 which will cause a slight change in the hitherto published diagnosis 

 of the family. 



Genus RHOMBOPORA Meek. 



Rhombopora Meek, Pal. Eastern Nebraska, 1872, p. 141. — Etheridge, Ann. and 

 Mag. Nat. Hist., ser. 4, vol. 20, 1877, p. 36.— Vine, Proc. Yorkshire Geol. 

 Polyt. Soc, vol. 8, 1883, p. 105. — Ulrich, Journ. Cincinnati Soc. Nat. Hist., 

 vol. 7, 1884, p. 26.— Vine, Proc. Yorkshii-e Geol. and Polyt. Soc, vol. 9, 

 1885, p. 93.— FoERSTE, Bull. Sci. Lab. Denison Univ., vol. 2, 1887, p. 71.— 

 Waagen, Mem. Geol. Snrv. India, Paleontologia Indica, ser. 13, vol. 1, 

 1888, p. 963.— Miller, North Amer. Geol. and Pal. 1889, p. 321.— Ulrich, 

 Geol. Surv. 111., vol. 8, 1890, pp. 402, 647; Zittel's Textbook of Paleontology 

 (Eng.ed.), 1896, p. 281. — Simpson, Fourteenth Ann. Rep. State Geologist New- 

 York for the year 1894, 1897, p. 550.— Grabau, Bull. Buffalo Soc. Nat. Hist., 

 vol. 6, 1899, p. 164.— Nickles and Bassler, Bull. 173, U. S. Geol. Surv,, 

 1900, p. 43. 



In this genus the zoarium consists of solid ramose slender branches 

 with the zooecial tubes in the vestibular region, thick-walled and 

 with numerous strong acanthopores and smaller spines. The aper- 

 tures are generally arranged in distinct longitudinal or diagonal lines. 

 The external aperture is oval or circular, and is usually situated at 

 the bottom of a rhombic or hexagonal sloping area. 



The following new species is remarkably like the Carboniferous 

 type of the genus, in fact, so far as can be determined from fossil 

 forms, is distinguished only by such minor characters as slight 



