180 THE PALEONTOLOGY OF MINNESOTA. 



[Sttctoporella. 



Tangential sections of favorably preserved specimens show that both the zocecia 

 and mesopores are separated from each other by a sharply defined line of minute 

 pore-like dots. True median tubuli and diaphragms wanting. 



Type : S. interstincta Ulrich. Range, Lower Trenton to Chester. 



For remarks on the relations and systematic position of this genus see ante p. 162. 



The range of zoarial diversity allowed in this genus is unusually comprehensive. 

 Perhaps it is too much so, and that the cribrose species ought to be distinguished 

 generically. Most certainly they look very different from the others and are, I grant, 

 as much entitled to generic separation as Clathropora, Hall, Coscinium, Keyserling, 

 and other genera that might be mentioned, all differing from related genera chiefly 

 or solely in the cribrose character of the zoaria. Though inclined to favor a sepa- 

 ration, I have decided to leave them with Stidoporella for the present 



CLASSIFICATION OF AMERICAN SPECIES. 



Section a: zoarium branching. 



Stidoporella interstincta Ulrich, Utica horizon, Cincinnati group, Kentucky. 



S. angularis Ulrich, base of Trenton shales, Minnesota. 



S. angularis var. intermedia Ulrich, base of Trenton shales, Minnesota. 



S. dumosa Ulrich, Trenton shales, Minnesota. 



S. rigida Ulrich, Trenton shales, Minnesota. 



Section b: zoarium wide, leaf-like, with maculae. 



Stictoporella frondifera Ulrich, base of Trenton shales, Minnesota. 



S. f basalis Ulrich, Keokuk group, Illinois, Iowa. 



S. f undulata Ulrich, Chester group, Kentucky, Illinois. 



Section c: zoarium cribrose. 



Stictopm-ella cribrosa Ulrich, middle Trenton shales, Minnesota. 



f Clathropora flabellata Hall, Trenton, Wisconsin. 



Stictoporella proavia (Coscinivm proavium Billings, ? Eichwald), Trenton, Canada. 



S. n. sp.fwith smaller meshes than in the others), "Pierce" limestone, Tennessee. 



STICTOPORELLA RIGIDA Ulrich. 



PLATE XI, FIGS. 20 and 21. 



Stidoporella ngida ULRICH, 1890. Jour. Cin. Soc. Nat. Hist., vol. xii, p. 188. 



Original description: "Zoarium a narrow branching, bifoliar stipe. Branches 

 flattened, 1.0 mm. or a litle more wide, with straight parallel and sharp margins, 

 acutely elliptical in cross-section. Zocecia in seven to nine or ten rows on each face, 

 their apertures arranged in very regular longitudinal and diagonally intersecting 

 series, with sixteen or seventeen in 5 mm. lengthwise and four in 1 mm. obliquely. 

 Apertures elliptical, 0.2 mm. long, half that wide, impressed, the sloping area narrow 

 for this genus, and appearing sometimes a little oblique because of a slight elevation 

 of the posterior border ; those in the marginal rows are directed slightly outward. 



