122 THE PALEONTOLOGY OF MINNESOTA. 



[Distribution. 



in these cases the Lower and Upper Silurian species are so nearly like the Secondary, 

 Tertiary, and recent forms of the genera, that a generic separation has so far seemed 

 impracticable. And yet, considering their apparent absence in the Devonian and 

 Carboniferous deposits, would we not be justified in denying the lineal descent of the 

 recent forms from the early paleozoic species ? However, questions of this kind can" 

 not be considered as they deserve in the space here at my disposal, and, as they are 

 also a little out of place in a publication of this kind, they will be merely touched 

 upon, leaving their real discussion for some more fitting occasion. 



DlASTOPORINA FLABELLATA Ulfich. 

 PLATE II, VIGS. 2 AND 3. 



Diastoporina flabellata ULRICH, 1890. Jour. Gin. Soc. Nat. Hist., vol. xii, p. 176. 



Zoarium small t arising from an attached basal expansion into thin flabellate 

 fronds. The largest and only complete example seen is 5.5 mm. wide. Surface 

 with obscure concentric wrinkles, and fine interrupted striations arranged parallel 

 with the direction of the zocecia. Under a high power of magnification the latter 

 appear as delicate lines separating rows of exceedingly minute pores. Zooecia rather 

 scattering, in young examples partly exposed, appearing as convex oval spaces with 

 a small oblique aperture, about 0.05 mm. in diameter and but little, if at all, elevated 

 at the distal extremity. In some fragments of seemingly older examples the entire 

 cell is immersed, leaving only the aperture, which, in these cases, is nearly direct 

 and subtubular, to project over the nearly even surface. Their arrangement is often 

 quite irregular, particularly in the vicinity of certain small non-celluliferous spots, 

 but where rows are to be made out, about six or seven apertures occur in 2 mm. 



This is the only bifoliate cyclostomatus bryozoan known to me in paleozoic 

 rocks. 



Formation and locality Rare in the Galena shales near Cannon Falls and at St. Paul, Minnesota. 

 At the first locality it is associated with a very interesting fauna, consisting principally of Ostracoda and 

 minute bryozoans, among the latter species of Nematopora, Helopora and Arthroclema. 



Genus MITOCLEMA, Ulrich. 



Mitoclema, ULRICH, 1882. Jour. Gin. Soc. Nat. Hist., vol. v, p. 150; and 1890, Geol. Sur. 111., vol. viii, 



pp. 336 and 369. 

 Comp. Clonopora, HALL, 1886. Pal. N. Y., vol. vi, p. 25; also, abstract Trans. Albany Inst., vol. x- 



p. 20, 1881. 

 Comp. Entalophora, LAMOUKOUX, 1821. Exp. nieth. des genres de pol., p. 81. 



Zoaria ramose, slender, subcircular in cross-section. Zooecia tubular, long, pris- 

 matic and thin-walled in the axial region, gradually diverging in all directions from 



