328 THE PALEONTOLOGY OF MINNESOTA. 



[Ceramoporella. 



The much smaller number of mesopores is the most obvious external difference 

 between the present species and A. ponderosa Ulrich. The lunarial tubuli also are 

 about twice as numerous in that species. Of Minnesota species, I know of only one 

 that is likely to be confounded. This is the Batostoma magnopora, a rare species of 

 the middle third of the shales (Rhinidictya beds), having, if not always monticules, 

 at least conspicuous clusters of large cells. The absence of such clusters in the 

 Anolotichia renders the separation of the two forms comparatively easy after all. 



Formation and locality. This is a very abundant and highly characteristic fossil of the lower 

 third of the Trenton shales at St. Paul, Minneapolis, Cannon Falls, Chatrfeld, Lanesboro and Fountain. 



Mus. Reg. Nos. 5958, 5962, 7660. 



Genus CERAMOPORELLA, Ulrich. 



Ceramoporella, ULRICH, 1882, Jour. Gin. Soc. Nat. Hist., vol. v, p. 156; Geol. Surv. 111., vol. viii, 



pp. 380, 464. 



Zoaria incrusting, often becoming massive by the superposition of numerous 

 thin layers. Zooecial tubes short, their walls thin. Apertures more or less oblique, 

 hooded, commonly of oval shape. The hoods are directed away from the centers of 

 small maculae marking the surface at rythmical intervals. Mesopores abundant, 

 often completely isolating the zooecia, their apertures usually open, sometimes closed 

 by a thin membrane. Diaphragms only rarely present. 



Type : C. distinda Ulrich, Cincinnati group, Ohio. 



This genus embraces all the parasitic Lower Silurian ceramoporoids. The 

 species, with few exceptions, are all closely related, and some of them seem also 

 to have an unusually extended vertical range. Thus the first of the following 

 Minnesota species, which occurs here in the lowest member of the shales, is so 

 much like the Cincinnati types of the genus that I cannot distinguish them. C. 

 inclusa is a well marked species, and unknown above the upper third of the Trenton 

 shales, but the Galena shales species, C. interporosa, n. sp., is likewise a common 

 form throughout the lower 300 feet of the rocks at Cincinnati, Ohio. 



CERAMOPORELLA DISTINCTA Ulrich. 





 PLATE XXVIII, FIG. 13. 



Ceramoporella distincta ULRICH, 1890. Geol. Surv. 111., vol. viii, p. 464. 



Zoarium forming thin parasitic patches upon other Bryozoa, the Minnesota speci- 

 mens seen consisting of but a single layer less than 0.7 mm. thick. Zooecia small, 

 radSally arranged about certain small maculae, nine to eleven, measuring obliquely, 



