132 THE PALEONTOLOGY OF MINNESOTA. ae 
[Rhinidictya. 
this is not the case. The latter are also exceptionally well preserved and show that 
the apertures are really rather strongly oblique, with a slight “lip” at the posterior 
border. Not in these specimens, even, have I detected satisfactory evidence of the 
presence of the row of granules on the longitudinal ridges usual in species of this 
genus. Yet, as is shown by thin sections, the minute inter-zocecial tubuli, whose 
superficial extension forms the granules, are developed in the usual manner, 
The obliquity of the zocecial apertures allies this species to the larger R. nichol- 
soni, but not closely enough to cause confusion between them. The zocecia are 
larger in that species, there being thirteen to fifteen where we have seventeen to 
eighteen in this form. It also resembles Rk. paupera and R. minima, but they are dis- 
tinguished: the first by having more ranges of zocecia with the apertures in several 
of the marginal rows on each side of the branches oblique ; the second by its smaller 
zocecial apertures and much wider granulo-striate interspaces. 
Formation and locality.—Comparatively rare in the lower third of the Trenton shales at Minneap- 
olis, St. Paul and near Fountain, Minnesota. 
Rernipicrya minima Ulrich. 
PLATE V, FIGS. 13-18. 
Rhinidictya minima Uuricn, 1890. Jour. Cin. Soc. Nat. Hist., vol. xii, p. 183, fig. 8. 
Zoarium small, branches 0.8 to 1.2 mm. wide, commonly 1.0 mm., bifurcating at 
intervals of 2 or 3 mm. Zocecia in five or six longitudinal rows, increasing to seven, 
eight, or nine before bifurcation takes place; sixteen in 5mm, lengthwise. Size and 
shape of apertures, and character of interspaces, varying with age. The enlarged 
figures on plate V represent the usual appearance of the oldest examples. In these the 
zocecial apertures are small and narrow-elliptical (about 0.11 mm. by 0.06 mm.) and the 
interspaces very wide, with the granulose ridges projecting but little above the level of 
the peristomes surrounding the apertures._ Under a glass of low power the interspaces 
appear as rather flattened, and marked with straight or slightly flexuous longitudinal 
strie. Under a higher power the striz resolve into rows of small papillie, with one 
continuous series, a little stronger than the others, separating the apertures into 
longitudinal rows, and one or two short series in the slightly depressed spaces 
between the ends of the apertures. When in a good state of preservation, a row of 
granules, rather smaller than the others, is found to crown the peristomes as well. 
These were overlooked in drawing fig. 15. In younger examples the principal longi- 
tudinal ridges are relatively higher, causing the zocecial apertures, which in these 
cases are wider, and the intermediate spaces to appear as set in shallow channels. 
Not infrequently the peristomes of succeeding zocecial apertures are connected in a 
