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, olocyst. 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. 

 Thirrf, 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." Fovrth, 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 easy 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 iintil 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. 



