216 THE PALEONTOLOGY OF MINNESOTA. 
|Monticuliporide. 
On plate XIX the figures up to No. 19 give an idea of the beginning of the line 
of development referred to in the latter part of the paragraph preceding the last. In 
Homotrypa minnesotensis we have what must still be regarded as a true species of the 
geuus.* Even here, as shown in fig. 3, a tendency to interpolate mesopore-like 
interspaces is occasionally manifest. In H. evilis this tendency is more strikingly 
expressed and permanent, (see figs 13-16), while in H. separata it has progressed to 
such an extent that the zocecia are rounded in shape instead of angular. These 
three forms all occur in the lower third of the Trenton shales. In the middle third 
we find a fourth stage in the development toward the Galena shales species provis- 
ionally called Homotrypella ovata. This fourth stage has been named Homotrypa (?) 
intercalaris and, as may be seen from the cut on a succeeding page, its characters are 
very nearly intermediate between those of the species separata and ovata. 
Difficulties like these were encountered -all through my work on the Minnesota 
Bryozoa, and now as it nears completion I realize, probably better than any one else 
can, that the result, despite my utmost efforts, is not final nor even entirely satis- 
factory in some parts. Had I followed my inclination and adopted a genealogical 
arrangement throughout it might have been better, because I believe it would have 
proven more permanent. But the criticism sometimes made that individual peculi- 
arities are magnified into specific, and specific into generic, seemed to indicate a state 
of knowledge not sufficiently advanced for the proper appreciation of all the innova- 
tions that it would have been necessary to enter into. Perhaps I ought not to have 
noticed criticisms which, like these, originate in ignorance of the fact that characters 
preserved in hundreds of specimens are not to be viewed as “individual.” But I 
have done so, and now must hope that the use of the interrogation point in cases of 
the kind discussed may be deemed sufficient for immediate needs. 
To prohibit repetition as much as possible I shall, in the course of the following 
pages, frequently refer the student to the preceding paragraphs. 
Family MONTICULIPORIDAt, Nicholson, emend. Ulrich. 
This family is strongly represented in the Lower Silurian rocks of Minnesota, there 
being here one or more species of every genus included in the family except Perono- 
pora, Nicholson. The individuals of the species too are generally abundant, especially 
those of Prasopora and Homotrypa, so that they constitute no inconsiderable part of 
the collections from the various horizons. 
*H, subramosa, illustrated on the same plate, is more nearly like the prevailing Hudson River group types of the 
genus. 
