THE

JOURNAL OF GEOLOGY

JANUARY-FEBRUARY, 1901

PROBLEM OF THE MONTICULIPOROIDEA. I.

THE Monticuliporoidea, comprising the greater part of the so-called Paleozoic Bryozoa, are a comparatively neglected group of fossils, as evidenced in such ways as frequent omission or slight mention of them in lists of fossils or descriptions of faunas. They are not, however, really without great scientific value, but rather their unpopularity may be due to the fact that at present there is a real difficulty for the amateur, the collector, or the geologist in making use of them; this difficulty being magnified, moreover, by a too readily accepted supposition that these fossils are for none but gifted specialists to study. In fact, the specimens themselves are very often excellent, the species quite easy to learn or to identify, and well worthy of consideration as to scientific value in geologic faunas, and the entire group is of peculiar interest to biology.

Aside from the retarding supposition that the Monticuliporoidea are difficult, the present difficulties attending them are these: (1) the interpretation of the animal that built the honeycomb-structured organic remains is still uncertain; (2) the monographs in which they are described want censorship; (3) study of the fossil involves technique more or less. These obstructions are, however, not absolute. It is the aim of this discussion to render them better understood, and hence less feared. Vol. IX, No. I.

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Regarding their interpretation, uncertainty exists to the extent that all Monticuliporoidea may be contested as not true Bryozoa, but Tabulata or Alcyonarian corals, belonging then to a different subkingdom of animals. This uncertainty may be illustrated as to its attendant difficulties by reference to Eastman's Text-book of Paleontology, Vol. I, where Prasopora, Neuropora, and many other genera appear twice, first under Cœlenterata and second under Bryozoa; the first following the text of Zittel, the second the authority of the translator's collaborator, who has taken the liberty to make some revision.

The fact that one cannot assert positively that species of the genus Prasopora and other genera were Coelenterates or were Bryozoons, is due to outward similarity of these two groups and obscurity in the fossils as to class characters. Yet structural details as to minor characters are well preserved, and hence the distinction of species and their grouping into genera is not impracticable here more than in many other groups, since species may be distinguished clearly in fossils as in living organisms. without knowledge of phylogenic relation to other classes. Ulrich, who considers them all as Bryozoa, and Nicholson, who treated them as corals, ought nevertheless to present the same determinations as to species, genera, and families. Their failure. to agree is not due to that cause. However, the former, in Eastman's translation of Zittel (op. cit.), presents as families of Bryozoa (viz., Calloporidæ, etc.) those which, following Nicho) son (vide op. cit., pp. 103-105), are given as genera Callopora, etc., of Cœlenterata. Understanding this discrepancy, the handbook is as useful respecting these as other groups, and the fossils are as easily used under its guidance. The student may choose his authority or follow a happy median course.

The lack of censorship in Eastman's Paleontology, just mentioned, may serve to argue further need of it in other places. S. A. Miller's catalogue divides the Monticuliporoidea species

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Text-book of Paleontology, by KARL A. VON ZITTEL, translated by Charles R. Eastman, 1900.

'S. A. MILLER, North American Geology and Paleontology.

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between Colenterata and Bryozoa. Of other chief works, especially those of Nicholson,' we may trust E. O. Ulrich to have criticised them fully. They are conservative and excellent, but inadequate for the study of American fossils without the magnificent recent monographs by E. O. Ulrich to supplement them. The last named, together with the chapter on Bryozoa in Eastman's Paleontology, would have offered a complete solution to the student for the study of the fossils and the involved problem of their affinities, if it were not for much obscurity in his definitions. One is compelled to criticise and to interpret anew from the fossils when endeavoring to follow him. In this connection it should be said also that the severe criticism of E. O. Ulrich, by S. A. Miller, op. cit., while touching his works on Paleozoic Bryozoa, does not appear to reach by censorship of the species this group as much or as well as other ones, for the reason, evidently, that his knowledge of them did not permit him. Therefore, while all species are listed as equally valid, some will be found, nevertheless, to have been made upon wholly insufficient evidence and require to be freely eliminated. The most species will again be far easier to identify than their descriptions would lead one to expect. It appears, in short, necessary to admit the value of some earlier criticism 3 of this author, and to expect to find similarities and differences described with acuteness, while fanciful values are frequently attached to them.

Regarding the handling of fossil Monticuliporoidea, one should collect all specimens and in the laboratory select the better preserved ones to begin with. These may be assorted and identified by means of external characters. A common hand lens will suffice to reveal whatever may be not clear to the naked eye. To be sure, the exhaustive study of the material requires the making and use of thin sections when practicable, for often only by that means can the also important internal 'H. A. NICHOLSON, On the Structure and Affinities of the Genus Monticulipora 1881.

2 Geol. Surv. Ill., Rept., Vol. VIII, and Geol. Surv., Minn., Final Rept., Vol. III. 3 ROMINGER, Amer. Geol., Vol. VI, pp. 103 and 120, 1890.

structure be discovered. The use of thin sections is, however, necessarily limited to special cases. These would be when a new species is in hand and all characters possible should be discovered; or, when a described species is illustrated and described chiefly as to its internal structure, which too frequently is the case; or, when the external characters have been obliterated. Having identified the species and referred it to a genus, etc., by use of all characters, further recognition of specimens of the same can and should, with rare exception, be made to depend on external characters alone. As in studying Brachiopoda, for example, one must know them by external characters, even though examination of internal structures is required to determine affinities of the species.

The advantage of learning to recognize the species, genera, etc., by external characters is in the saving of time, since thousands can be examined in that way, while sectioning limits the labor of one man to at most twenty specimens per day; knowledge of the range and variability of one and many species is made practicable; it serves to direct to best advantage the use of thin sectioning; recognition of species even in the field becomes thereby entirely practicable. Having learned to know a group of species, or the fauna of a locality or of a zone, the specimens may be identified thereafter without the use of sectioning, and the difficulty of technique may be obviated by the geologist.

Thin sections of fossils may be made by the same process as bone or rock sections are ground, which need not be described here. It requires less skill, however, since they should not be ground to absolute thinness. Some simple appliance for measuring the cell dimensions is also needed.

Pains may be saved by attention in collecting, since each bed or zone may have a large proportion of species peculiar to it, and by avoiding mixing fossils of different zones, labor of again assorting is saved.

TREPOSTOMATA

A few selected species may illustrate what is to be looked for in Monticuliporoidea. Beginning with Trepostomata one

then has to do with the most problematic as to affinities of the so-called Paleozoic Bryozoa, i. e., those which most resemble corals, proceeding then to those often supposed to be true Bryozoa, the Cryptostomata. Eastman's manual, op. cit., includes them in the arrangement given below, and in the Order Gymnolæmata, which comprises most Bryozoa and all known fossil ones. Of those five divisions, the last named, Chilostomata, are all undoubtedly Bryozoa, but are not known in the Paleozoic rocks. The first, Cyclostomata, are, with few possible exceptions, all true Bryozoa, but few of them are Paleozoic. The second, third, and fourth comprise the Monticuliporoidea.

1. Cyclostomata (8 families).

2. Families doubtfully referred to Cyclostomata (4 families).

3. Trepostomata (7 families).

4. Cryptostomata (8 families).

5. Chilostomata (13 families).

In that arrangement those of doubtful affinities are embraced between the true Bryozoa. A fairer presentation of the problem may be given thus:

Tabulata (corals)-Trepostomata (?)-Cyclostomata (bryozoa)

and it is in such association that the Monticuliporoidea should be studied. The group of "Doubtfully referred to Cyclostomata" are Trepostomata.

Beginning with one of the simpler Trepostomata,

Monotrypa magna Ulr. has a skeleton or zoarium one or two inches in diameter, composed of tubes or "cells" which radiate from an approximate center. It is nearly spherical if growing attached on one point, or discoid if on a flat surface, or, again, irregular. The center is the initial or oldest part, and from it one, or practically several, cells arise, and as these extend, others intercalate successively. A specimen divided radially (Pl. A, Fig. 2) shows parallel, approximately equal, cells, each tapering to a point at the inner end. The plan of growth is that of increase in number of cells proportionate to the increase in size of the zoarium. At the surface, the open cell ends are