130 THE PALEONTOLOGY OF MINNESOTA. 



[Rlilnidlctya. 



peristome ; (2) the interspaces on the whole are thicker, while the elevated lines 

 enclosing the depressed quadrangular spaces in which the apertures are situated, are 

 sharper; (3) the arrangement of the apertures between longitudinal lines prevails 

 throughout, there being no oblique rows ; and (4) while the width of the branches is 

 about the same or greater (the average is very nearly 1.5 mm.); there are only seven 

 to nine rows of cells instead of ten to twelve. In all these respects, however, the 

 Canadian form agrees more closely with R. neglecta, but before I commit myself def- 

 initely upon the matter of their true relations I shall want to institute careful 

 comparisons of their respective internal characters a step that I am not yet pre- 

 pared to make. Still, in the meantime, it may be desirable occasionally to refer to 

 the Canadian form, in which case a distinctive appelation would be convenient. I 

 propose, therefore, the provisional designation Rhinidictya negleda, var. canadensis. 



Comparing R. paupera (sens, strict) with other species of the genus, we find that it 

 is distinguished from R, mutabilis by its smaller zoarium, narrow and more frequently 

 dividing branches, more numerous zooecia in a given space, and the greater differen- 

 tiation in the direction of the central and marginal zooecial apertures ; from R. trenton- 

 ensis and R. nicholsoni in much the same features, though in a different degree. To 

 them is to be added, for the former, that its zoo3cial apertures are not only much 

 larger, but more nearly quadrate or hexagonal, with the longitudinal ridges between 

 them nearly or quite obsolete ; and for the latter, that its zooecial apertures are 

 more oblique. E. exigua is very close, differing mainly in its narrower branches and 

 less oblique arrangement of its zooecial apertures in the marginal rows. R. minima 

 has thicker and more ornamental zooecial interspaces, and differs internally in hav- 

 ing the superior hemiseptum well developed. 



Formation and locality. Not uncommon in the upper third ("Phylloporina beds") of the Trenton 

 shales, at St. Paul and south of Cannon Falls, Minnesota, and Decorah, Iowa. Probably also in the 

 Galena at Neenah, Wisconsin. 



Mus. Reg. Nos. 5935. 7564, 7612. 



RHINIDICTYA NEGLECTA, n. sp. 



PLATE V, PIGS. 23-23. 



Stiotopora paupera (part.) ULKICH, 1886. Fourteenth Ana. Kept. Geol. Nat. Hist. Sur. Minn., p. 69. 



Zoarium small, branches dividing dichotomously at intervals of from 4 to 7 mm., 

 rather convex, the margins parallel, not very sharp, and with the non-celluliferous 

 border variable. Width of branches rather constant at about 1.5 mm. Zooecia in 

 eight to eleven ranges, the usual number nine, with rather small, elliptical ; oblique 

 apertures, about seventeen in 5 mm. lengthwise, and 6 in 1 mm. transversely. In 

 most cases all the apertures are directed longitudinally or parallel with the edges 



