284 THE PALEONTOLOGY OF MINNESOTA. 
(Callopora pulchella var. presimilis. 
smaller zocecia. Excepting the following variety there is no Minnesota species of 
Callopora known that is likely to be confounded with C. pulchella, but care is required 
in separating it from the associated Homotrypa tuberculata. 
Formation and locality—Common in the upper third of the Trenton shales at St. Paul and near 
Cannon Falls, Minnesota. 
Mus. Reg. Nos. 8033, 8114. 
CALLOPORA PULCHELLA, U@?, PERSIMILIS, ”. Var. 
PLATE XXII, FIGS. 13-17. 
This variety differs from the typical form of the species in having more prom- 
inent tubercles, thinner zocecial walls (causing the apertures to be correspondingly 
larger), more readily distinguished and, as a rule, more numerous mesopores, even 
fewer diaphragms, and in the greater size of the tubes in the axial region. The 
growth of the zoarium and the number of zoccial apertures in 3 mm. (thirteen or 
fourteen) is the same. Indeed, the points of difference even are not constant. We 
cannot, therefore, doubt the propriety of referring the form to C. pulchella. On the 
other hand it is impossible to distinguish var. persimilis, by external comparison of 
fragmentary material alone, from the later C. ramosa d’Orbigny, one of the most 
common Bryozoa of the Cincinnati rocks. It is true the zoaria of the Trenton form 
never grew to such a size nor do the branches inosculate as in the Cincinnati species, 
but such differences the student will find of little practical use when, as usual, frag- 
ments are to be identified. Luckily, the interior furnishes us with a guide in the 
relative number of diaphragms, these being much more abundantly developed in the 
Cincinnati species than in the Trenton variety. For further remarks relating to 
this subject see ante. p. 215. 
Formation and locality.—Associated with Phylloporina corticosa, Trigonodictya conciliatrix and 
Prasopora conoidea, all characteristic species of the upper third of the Trenton shales, at Poe’s farm, 
near Cannon Falls, Minnesota. 
Mus. Reg. No. 8115. 
CALLOPORA CRENULATA, 7”. Sp. 
PLATE, XXII, FIGS. 18-23. 
Zoaria forming rather large, compactly interwoven, bushy masses, consisting of 
strong branches that divide and inosculate most irregularly and frequently; average 
thickness of branches 7 or 8 mm., but some may be over 10 mm., and as many only 
4 or 5 mm. Surface generally with rounded monticules, occupied by clusters of 
zowecia larger than the average, and by greater or less aggregations of small meso- 
