134 THE PALEONTOLOGY OF MINNESOTA. 
[Rinidictya. 
Ruripiorya FIDELIS Ulrich. 
PLATE. VI, FIGS. 7, 7a, 7b AND §. 
Stictopora jldelis (part), ULRicH, 1886. Fourteenth Ann, Rep. Geol. Nat. Hist. Sur. Minn., p. 68. 
To save repetition it will suffice to say of the external characters of this species 
that they are exceedingly like those of the next described RP. trentonensis, a slightly 
greater width of the also more nearly quadrangular zocecial apertures, being rather 
inconspicuous differences. 
In tangential sections the deepest parts show the prostrate portion of the zocecia 
lying on each side of the mesial laminew. The latter themselves may be shown as 
in fig. 7b with the inclosed “median tubuh.” ‘These horozontial tubuli seem to con- 
nect with the vertical sets that form series separating the rows of zocecia., At first 
the zocecia appear as simple quadrangular spaces, their width equalling about half 
of the length. In the next stage these spaces are divided by a line, transversely in 
the central rows, and obliquely upward in the marginal ranges. This line represents 
the incurving superior hemiseptum, which is developed to an unusual degree in this 
species. In the stage immediately succeeding, the posterior half is covered, while 
the open anterior part is gradually reduced in width till it assumes the elliptical 
shape commonly presented by the “vestibular” portion of the zocwecia. From now 
on to the surface, the distance depending upon the age of the specimen, the section 
exhibits little if anything to distinguish it from similar sections of other species, 
There are rows of subelliptical apertures separated by thick interspaces, and between 
the rows a dark, faintly flexuous line, which, when carefully examined, is found to 
contain a series of minute pores. 
Vertical sections are highly characteristic, especially when they have been care- 
fully prepared and show the primitive region of the zocecia in a satisfactory manner. 
The anterior side of the zoccial cavity is almost straight from the mesial lamina to 
the superficial aperture. The posterior and upper side is concave and the curve 
produced in front into a strongly developed hemiseptum, projecting over half the 
distance toward the base of the anterior wall. An occasional complete diaphragm- 
like structure may be detected crossing the tubular vestibule. All of these char- 
acters are shown very well in fig. 8. 
As has been stated, it is not an easy matter to distinguish this species, by means 
of external characters alone, from R. trentonensis, and until the observer has become 
thoroughly familiar with the various forms of this genus occurring in the Minnesota 
rocks, he is cautioned to secure the evidence of thin sections before he places much 
confidence in his identification, of this species, at any rate. The strongly developed 
