144 THE PALEONTOLOGY OP MINNESOTA. 



[Phyllodiotya. 



differences are to be found in the character of the interspaces, and in the shape of 

 the zoarium. 



Formation and locality.— Ua,Te in the Trenton shales, at Minneapolis, Minnesota. The types of the 

 species are from the Birdseye limestone at High Bridge, Kentucky. 



Phyllodiotya vaeia, n. sp, 



PLATE XIV, FIGS. 1-8. 



Comp. Stictopora lahyrinthica Hall, 1847. Pal. N. Y., vol. i, p. 50. 



Zoarium variable, consisting of broad, leaf-like, thin expansions, either simple 

 or with irregular marginal incisions, or of wide branching fronds, with the edges 

 subparallel, sharp, and non-poriferous. At intervals of about 4 mm. the surface 

 exhibits subsolid, even or slightly depressed spots or " maculae," smooth when worn, 

 finely grano-striate as well as faintly channeled longitudinally when well preserved. 

 In the youngest examples these maculae are small and sometimes scarcely distinguish- 

 able, but with age they seem to increase in size (compare figs. 2 and 7). The most 

 obvious and normal arrangement of the zooecial apertures is in longitudinal series, 

 twelve or thirteen in 5 mm., between delicate papillose ridges ; but the general 

 aspect of the surface varies greatly in the specimens before me. Some of these dif- 

 ferences are doubtlessly due to, or exaggerated, by weathering and other accidental 

 causes, yet others are as clearly changies consequent upon increasing age, and thus 

 are to be regarded as expressing different stages in the development of the zoarium. 

 In the youngest the zooecial apertures are very oblique, with a rim, strongly elevated 

 at the posterior side, and dying out at the sides or seeming to unite with the delicate 

 ridges separating the rows. This condition is represented in figs. 2 and 3. In later 

 stages the longitudinal ridges becomes indistinct, the interspaces flatter, the poster- 

 ior "lip" less pronounced, the apertures less oblique and, sometimes, a little smaller, 

 while in other cases, probably representing a weathered condition, they appear 

 larger, with the interspaces rounded. The longitudinal arrangement also becomes 

 less obvious but never, so far as observed, quite subordinate to the diagonal. This 

 may seem to have occurred over limited spots, especially when the maculae are unusu- 

 ally large as in the specimen represented by figs. 6 and 7. 



Only one specimen proved suitable for sectioning. This even failed to preserve 

 the minuter details of structure as well as was desired. So far as the internal char- 

 acters could be made out they are shown in figs. 4 and 5, excepting that by an unac- 

 countable oversight the diaphragms were not drawn in the vertical sections. Each 

 tube should have shown one diaphragm crossing it at right angles at a point about 

 midway between its aperture and the mesial line. 



