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. 



SPATIOPOKA LABECULOSA, n. sp. 



PLATE XXVIII, FIGS. ) 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. 

 Zocecial 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 maculae. 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 zooecia eleven to 

 thirteen occur in 3 mm. Mesopores varying in number and distribution, but some- 

 thing like the following rule seems to prevail. When the maculae 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 maculae. 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 tills 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 Ohatfield, Minn. The specific characters 

 of these specimens, which grew over the shells of a small Orthocerax, are very similar to those of S. maculosa and S. lineata 

 Ulrich. of the Cincinnati rocks, As a provisional designation for the form I would propose the name S. mocuiosa, var. 

 incpta. 



