6 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
work of sieving the sand, and a small pill box was sufficient to hold the entire 
results. 
In case these fossils can not be found in soft rock, it is often still possible to 
obtain good specimens for study. A comparatively hard fossiliferous rock when 
crushed in a sack with a wooden mallet will often afford fairly well-preserved 
fossils after the debris has been washed and sieved as mentioned above. In such 
a case the bryozoans, although likely to be broken into smaller fragments than 
usual, are generally well enough preserved for accurate determination. If the 
rock is calcareous and too hard to yield to such treatment, thin sections may be 
employed to determine the bryozoa. If the matrix be siliceous the fossils are almost 
invariably present as molds, in which case gutta-percha squeezes afford excellent 
results. 
The separation into species of the fragmentary specimens resulting from the 
washings can be made with an ordinary hand lens magnifying eight or ten 
diameters. The identification of these species can also be made under such a 
lens providing the species have already been well described and illustrated. In 
the identification and discovery of the characters of new species, however, a higher 
magnification is necessary, and also some special sections must be prepared. 
First , thin sections of the walls, particularly the frontal, are needed to illustrate 
the characters of the three layers, olocvst, tremocyst, and pleurocyst. Second , the 
frontal must be abraded away to show the occurrence of such structures as dietellae. 
This abrasion is effected by mounting the fossil, frontal side up, in Canada balsam 
on a slide and after heating to harden the balsam, rubbing it gently on a soft hone. 
Third ', by the preparation of a similar section the interior of the frontal side can be 
studied. Calcification on the frontal frequently obscures, the true form of the 
apertura and its accompanying structures. These are all well preserved on the 
.inner side of the frontal, so by mounting the fragment in balsam, outer face down, 
and rubbing away the opposite side, the structure of the interior is clearly revealed. 
Throughout the description in the present work this section is spoken of as “ in the 
interior.” Fourth , a section passing lengthwise through the zooecia or individual 
cells is necessary to determine the nature of the ovicell as well as the general 
structure. This section requires much care, as the specimen must be mounted on 
edge and the abrasion must follow a definite row of cells. By the use of small wire 
nippers it is eas} r to trim the specimen to just the right form, then by mounting it 
in hardened balsam between two small bits of wood (fragments of a match serve 
excellently) to hold it on edge, the abrasion can be continued until the desired 
section is obtained. Fifth , actual dissection of the fossil specimens with a fine 
needle under the microscope is often necessary, especially to determine the nature 
of the ovicell. 
It will now be evident that the description of the small openings on a fossil 
bryozoan is the least part of their study and that as refined methods of research 
may be employed on these microscopic forms as on any other class of animals. 
