320 THE PALEONTOLOGY OF MINNESOTA. 
[Spatiopora labeculosa. 
Two Trenton species, S. areolata Foord, and S. labeculosa Ulrich, are referred to 
the genus with doubt.* The type, together with four or five other species, is found 
in the Cincinnati or Utica and Hudson river groups, above which the genus is not 
known to pass. 
SPATIOPORA LABECULOSA, %. Sp. 
PLATE XXVIII, FIGS, J and 2. 
Zoarium forming large and very thin expansions generally upon Orthoceras or 
Endoceras. Surface even, but conforming with the irregularities of the body grown 
upon. At intervals of 4 or 5 mm., measuring from center to center, there are 
clusters of cells decidedly larger than the average. These large apertures—they 
vary from 0.25 to 0.50 mm. in diameter—are arranged in each case about a sub- 
stellate or irregular, apparently solid, spot, which on closer examination proves to 
consist of closed mesopores. The extent of these spots varies greatly, some being 
almost 2 mm. wide, while in others the center is scarcely more than 0.5 mm. wide. 
Zoccial apertures subangular, usually a little oblong, with the margin on one side 
generally a little higher and more rounded than on the other. The last is true more 
particularly of the large cells which are not infrequently decidedly oblique and 
directed away from the center of the macule. In very young examples all of the 
apertures may be quite as oblique as in some species of Ceramoporella, but the 
lunarium is ever an inconspicuous feature. Many of the large cells again may 
preserve peculiar convex closures. Of the smaller or average zocecia eleven to 
thirteen occur in 83mm. Mesopores varying in number and distribution, but some- 
thing like the following rule seems to prevail. When the macule are large the 
mesoposes are few and of small size elsewhere (see figs. 1 and 2); when small they are 
comparatively more abundant in the inter-macular spaces. 
Internal characters: Figure 2 is a faithful copy of a portion of a tangential 
section prepared from a specimen (fig. 1 is an enlargement of its surface) having 
large macule. It will be noticed that the side of the zocecia nearest the macula is 
nearly always less angular than the opposite side. This fact is good evidence of the 
possession of an incipient or undeveloped lunarium. The minute structure of the 
walls, which is not the same as in Leptotrypa, is likewise indicative of ceramoporoid 
affinities. In vertical sections the prostrate part of the tubes is rather short, and 
the erect part, forming an angle of about 80° with the line of the surface, perhaps 
* Since this report was placed in the hands of the printer, two specimens of a typical species of this genus were collected 
by the author in the upper part of the middle third of the Trenton shales at Chatfield, Minn. The specific characters 
of these specimens, which grew over the shells of a small Orthoceras, are very similar to those of S. maculosa and S. lineata 
Ulrich, of the Cincinnati rocks, As a provisiona] designation for the form I would propose the name S. maculosa, var. 
incepta, 
