270 THE PALEONTOLOGY OF MINNESOTA. 



fDekayella. 



genus. The chief reason for doing so is that with the great abundance of material 

 specific, varietal and individual studied, an almost complete chain may be made 

 out connecting one with the other. But, as I have had occasion to state more than 

 once heretofore (ante pp. 115, 138, 216), this is not a sufficient reason for uniting two 

 or more genera. The groups of species embraced in each are natural and in a great 

 measure readily distinguished, and therefore must always be recognized in some 

 manner. Heterotrypa, as restricted and used by me, includes only frondescent or 

 palmate zoaria, with all the acanthopores small and approximately of one size; 

 Dekayia, subcylindrical or flattened stems growing from a large base, with one set 

 of acanthopores, mesopores very few or wanting, and few diaphragms in the tubes; 

 and Dekayella, zoaria as in Dekayia, but with acanthopores of two sizes, mesopores 

 more or less numerous, and abundantly tabulated tubes. 



DEKAYELLA PR^ENUNTIA, n. sp.; and VARIETIES. 



PLATE XXIII, FIGS. 32-47. 



Compare Heterotrypa ulriehii NICHOLSON, 1881, " Genus Monticulipora," p. 131. 



Typical form : Plate XXIII, fig. 43. 



Zoarium ramose ; branches subcylindrical, often compressed, dividing at irregu- 

 lar intervals, varying in diameter or width from 4 to 12 mm. Surface without 

 monticules, but in well-preserved specimens minutely spinulose ; clusters of large 

 cells inconspicuous. Zooecial apertures obscurely angular or rounded, enclosed by 

 moderately thin walls, averaging about thirteen in 3 mm. Mesopores not very 

 numerous, generally one to each zooecium, rather irregularly distributed, often 

 forming small clusters. Acanthopores small, about half the number of zooecia. 



Internal characters: In vertical sections the tubes are nearly vertical in the 

 axial region, and here are crossed by diaphragms at interval equalling two to four 

 times their diameter. As the tubes bend outward an occasional acanthopore may 

 be detected, while the intervals between the diaphragms become less, until in the 

 fully matured peripheral region, in which the tubes are directed nearly at right 

 angles to the surface, the average distance between them is about one-half their 

 diameter. It is in the latter region that the mesopores are developed. These are 

 distinguished by their smaller size and more crowded diaphragms. An obscurely 

 beaded wall-structure, as shown in fig. 40, with overlapping diaphragms, is of com- 

 mon occurrence. 



Tangential sections show that the zooecia are mostly oval or rounded, their walls 

 of variable thickness, and in part separated by intervening mesopores. The latter 



