136 THE PALEONTOLOGY OF MINNESOTA. 



[Rhinidictya. 



first of those species it differs mainly in its wider and nearly direct zooecial aper- 

 tures and narrow interspaces, these being also without surface granulations so far 

 as observed. Still, some of the Minnesota specimens referred here resemble R. 

 nicholsoni more closely than do the Tennessee types. It is therefore not improbable 

 that more detailed comparisons than I have found time to make may show that, as 

 T believed in 1886, R. nicholsoni also is represented in the Minnesota strata. R. grandis 

 is readily distinguished by its wider branches and larger cells. R. pediculata likewise 

 seems closely related, but its peculiar growth and somewhat wider branches will, it 

 is believed, serve to separate them. Lastly, R. fidelis so closely resembles this species 

 in its external characters that I am at a loss to point out really serviceable distin- 

 guishing features. As a rule the zooecial apertures of R. trentonensis are a trifle nar- 

 rower and less often of quadrate shape. Comparing their internal characters, we 

 at once notice a decided difference in the inner part of the zooecia where that species 

 presents a well developed superior hemiseptum. This is a point of such importance 

 that I am obliged to view the two species as widely distinct. 



Formation and locality. "Glade" limestone (Birdseye) at Lebanon, Tennessee; lower third of 

 Trenton shales at Minneapolis, Minnesota. Rather rare. It has also been collected by Mr. C. Schuchert 

 in the "Lower Blue beds" at Janesvillo, Wisconsin, and Eockton, Illinois. 



Mus. Reg. Nos. 7549, 7560. 



BHINIDICTYA GRANDIS n. sp. 

 PLATE v, FIGS. 11 and ia ; PLATE vi, FIGS. 10 and 20. 



Zoarium bifolate, large, branchy, the branches flattened, 2.5 to 3.5 mm. wide, the 

 edges obtuse, with the non-poriferous margin of moderate width. Zooecia in from 

 eleven to fifteen alternating rows, with large, almost direct, slightly oblong, hexa- 

 gonal apertures, fourteen or fifteen in 5 mm. longitudinally, and nine of the central 

 rows in 2 mm. transversely. Interspaces thin, without papillae, ridge-shaped, sloping 

 down into the apertures from the summit, the latter reaching to about the same level 

 in both the cross and longitudinal partitions. In conforming with the hexagonal 

 shape and alternate arrangement of the zooecial apertures, the longitudinal walls 

 usually take a decidedly zigzag direction. In the marginal rows the apertures are 

 commonly more or less irregular in shape, size and arrangement. An occasional 

 small cell may be noticed. 



In vertical sections the comparative erectness of the zooecia is to be noticed; 

 also the shape of the walls. These show no sign of a superior hemiseptum, though 

 a slight angularity is often perceptible at the turn into the vestibular region. 



