204 ■ THE PALEONTOLOGY OF MINNESOTA. 



[Nematopora. 



vails. The surface is striated, especially on the more regularly constructed segments, 

 very much as in A. pulchellum. Though inclined to regard it as an illy nourished 

 variety of that species, with shorter and more slender segments, I- prefer, for the 

 present, to leave the form unclassified specifically. 



All the specimens of this form were collected by ttie in the upper part of the 

 Trenton shales at St. Paul, Minnesota. 



Genus NEMATOPORA, Ulrich. 



Nematopora, Ulkich, 1888, The American Geologist, vol. i, p. 234; 1890, Illinois Geol. Surv., vol. viii, 



pp. 401 and 644. 



Zoaria very slender, branching, continuous above the pointed basal extremity. 

 Zocecia subtubular, short, arranged in a radial manner around one or two exceed- 

 ingly minute axial tubes. Apertures arranged in longitudinal series between smooth 

 or granulose ridges, nearly direct, generally elongate-ovate and enclosed by a thin 

 peristome. One or two diaphragms occasionally present. 



Type : N. ovalis Ulrich {N. quadrata Ulrich, 111. Geol. Surv., vol. viii, 1890). 



Of this genus we now know about fourteen species. Seven of these are from 

 Trenton rocks, one (undescribed) from the Cincinnati and Hudson River groups, five 

 from the Anticosti, and one, N. minuta Hall, sp., from the Niagara of Indiana. 



The genus differs conspicuously from the other generic types included in the 

 Arthrostylidce in having the zoarium continuous and dichotomously branched, the 

 jointed character prevailing in the family being confined to the basal extremity. 

 This part of the zoarium is, however, known of only one or two of the species, and 

 it may yet be proven that in some of the species there is no basal articulation. But 

 in the meantime, especially since the various forms agree very closely in ^ooecial 

 features, we may assume that the lower extremity was pointed and articulated with 

 a small basal expansion. The relations to Helopora, Hall, are therefore very nearly 

 the same as between Escharopora, Hall, and Arthropora, Ulrich. 



Nematopora ovalis Ulrich. 



PLATE III, FIGS. 24 und 25. 



Nematopora ovalis Ulkich, March, 1890. Jour. Cin. See. Nat. Hist., vol. xii, p. 197. 

 Nematopora quadrata Ulrich, Dec, 1890. 111. Geo. Surv., vol. viii, p. 644. 



Original description: "Zoarium ramose; branches birfurcating at intervals of 

 about 2 mm., 0.3 to 0.4 mm. in diameter, subquadrangnlar or pentagonal in cross- 

 section, each face with a row of zooecia. Zooecial apertures direct, very large, oval, 

 nearly 0.3 mm. long by 0,15 mm. wide, enclosed by a sharply defined peristome, A 



