270 THE PALEONTOLOGY OF MINNESOTA. 
(Dekayella. 
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 PRENUNTIA, 7. Sp.; and VARIETIES. 
PLATE XXIII, FIGS. 32-47, 
Compare Heterotrypa ulrichii 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. Zocecial apertures obscurely angular or rounded, enclosed by 
moderately thin walls, averaging about thirteen in 3 mm. Mesopores not very 
numerous, generally one to each zocecium, rather irregularly distributed, often 
forming small clusters. Acanthopores small, about half the number of zocecia. 
Internal characters: n vertical sections the tubes are nearly vertical in the 
axial region, and here are crossed by diaphragms at intervals 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 zocecia are mostly oval or rounded, their walls 
of variable thickness, and in part separated by intervening mesopores. The latter 
