BRYOZOA. 281 
Callopora ampla.] 
The diaphragms are more numerous in this species than in any other known to 
me. Very closely allied, however, are C. angularis, C. ampla and C. goodhuensis. The 
first is distinguished by its smaller size, smooth branches and somewhat less crowded 
diaphragms, especially in the mesopores; the second by its smooth branches, nar- 
rower peripheral region, slightly larger zocecia and more numerous mesopores; the 
third is smaller, with smaller zocecia and more abundant mesopores. 
Formation and locality.—In Minnesota the species is rare in the middle third of the Trenton shales 
at Minneapolis, rather abundant in the upper third at St. Paul and in the vicinity of Cannon Falls, and 
exceedingly abundant in the Galena shales at many localities in Ramsey, Goodhue and Fillmore counties. 
Also a common fossil of the Trenton at several localities in central Kentucky, and near Nashville, Ten- 
nessee. The same species apparently occurs at Ottawa, Canada. 
Mus. Reg. Nos. 3485, 7652. 
CALLOPORA AMPLA, 2. Sp. 
PLATE XXIII, FIGS. 15, 18-20, 22, 23, 27, 28. 
This form is very closely related to C. multitabulata, and doubtlessly belongs to 
the same line of development. Under the circumstances it will be sufficient to 
point out its peculiarities. The growth is less compact, the branches, though fully as 
large as in that species, being, as a rule, less frequently divided. Except in rare cases 
the surface is without monticules, and while there are clusters of zocecia appreciably 
larger than the average they are never conspicuous except when elevated into mon- 
ticules. The zocecia are larger, with an average of nine in 3 mm., the apertures a 
little oblique, drawn out lengthwise and apparently more shallow, while the occa- 
sionally preserved closures seem to be without ornamentation. The form of the 
apertures may be oval or angular, the first when mesopores are comparatively 
abundant, the second when they are few and very small. In both cases, however, 
thin sections are generally required to demonstrate the existence of the latter. In 
most instances the mesopores are fewer than in fig. 18, and as a rule they occupy the 
angles of junction between the zocecia where, when the surface is a little weathered, 
they often appear as acanthopore-like elevations. 
Comparing internal characters we find that in C. ampla the tubes in the axial 
region are generally of larger size, and that they curve to the surface more slowly. 
The fully developed peripheral region is much narrower than in specimens of the 
same size of C. multitabulata (compare figs. 19 and 22 with 24 of plate XXIII), the 
superficial crowding of the diaphragms more sudden, and the intervals between 
them throughout the axial region a little greater. The last difference, however, 
does not apply when we compare the Galena shales varieties of the two species. 
These often agree so closely in every other respect as well that a rigid distinction 
