EAELY PALEOZOIC BRYOZOA OF THE BALTIC PROVINCES. 69 



relatively more expanded at their anterior end, differences which 

 the study of more material will probably remove, and which are 

 insufficient for the recognition of even a variety. 



Occurrence. — The earliest appearance of C. dissimilis is in the Lyck- 

 holm limestone (Fl), at Kertel, island of Dago (Cat. No. 57112, 

 U.S.N.M.). It has also been found in the Borkliolm limestone (F2) 

 at Borkliolm, Esthonia (Cat. No. 57113, U.S.N.M.). The types of the 

 species are from the Buildwas beds of the Wenlock shales, Shropshire, 

 England. The species occurs also in the SUurianbeds, island of Goth- 

 land, where it has been given the name Stomatopora minor by Hennig. 

 It is abundant in the Rochester shales at Lockport and other locali- 

 ties in western New York, and at Grimsby, Ontario, and in the Os- 

 good beds at Osgood, Indiana. 



Family ENTALOPHORID^ Reuss. 



The Entalophoridge comprise ramose Cyclostomata \vith the circu- 

 lar apertures exsert and opening on all sides. The single genus 

 discussed in the present paper was instituted for American Paleozoic 

 forms and has been placed by some writers as a synonym of the recent 

 genus Spiropora Lamouroux, but the latter, according to Ulrich, has 

 a definite central axis from which the zooecia originate, wliile, in 

 species of Mitoclema, this axis is absent and the tubes have their 

 origin in the manner of ordinary ramose forms. These two genera, 

 although probably closely related, exhibit the same differences dis- 

 tinguishing genera in other families. 



Genus MITOCLEMA Ulrich. 



Mitoclema Ulrich, Journ. Cincinnati Soc. Nat. Hist., vol. 5, 1882, p. 150; Geol. 

 Surv. Illinois, vol. 8, 1890, pp. 336, 369; Geol. Nat. Hist. Surv. Minnesota, vol. 

 3, pt. 1, 1893, p. 122. — Simpson, Fouxteenth Ann. Rep. State Geologist New 

 York for the year 1894, 1897, p. 598.— Nickles and Bassler, Bull. 173, U. S. 

 Geol. Surv., 1900, p. 22.— Bassler, Bull. 292, U. S. Geol. Surv., 1906, p. 18. 



Zoarium ramose, cylindrical, consisting of long tubular zooecia, 

 which are thin-walled and prismatic in the axial region, diverge 

 gradually from the center, and bend abruptly outward near the 

 surface, often becoming free and much exserted; apertures terminal, 

 circular, usually arranged in regular transverse or subspiral series. 



Genotype. — Mitoclema cinctosum Ulrich. Middle Ordovician of 

 Kentucky and Tennessee. 



MITOCLEMA BOREALE, new species. 



Plate 6, fig. 8; text fig. 15. 



Zoarium of small, ramose, cylindrical, frequently bifurcating 

 branches, averaging 0.8 mm. in diameter. Interzooecial surface 

 smooth, minutely but clearly porous. Zooecia tubular, with rounded 

 apertures, 0.15 mm. in diameter, projecting only slightly above the 

 general surface of the branch, and arranged in ascending spiral rows. 



