NORTH AMERICAN EARLY TERTIARY BRYOZOA. 5 



at present study these interesting animals. The paleontologist who has not followed 

 closely the development of all these researches and who is not himself a trained 

 zoologist is absolutely powerless to prepare a useful work. On the other hand, a 

 large paleontologic work prepared by a competent zoologist would be little com- 

 prehended by the readers, since they have not been able to study any comprehensive 

 work embodying the more important progress in bryozoology. 



The present writers were therefore in a quandary since by preparing a strictly 

 paleontologic monograph they ran the risk of publishing a work incomprehensible 

 and discouraging to students and collectors alike. In order to avoid such a result 

 they decided to closely associate the paleontology and zoology of the bryozoa by 

 the introduction of numerous text figures, wherein the more recent work concern- 

 ing each of the. families and genera considered is illustrated. Naturally this is not 

 as comprehensive a zoologic work as could be desired, but it is sufficient for the 

 exact interpretation of the structure of the Tertiary bryozoa of American strata. 

 This has been supplemented by lists of recent and fossil species under each genus. 

 No attempt has been made to classify all the known species, but the lists are simply 

 complete enough to remain exact. 



The terminology of the bryozoa has become somewhat specialized, although it 

 is still far from being very complicated. The reader will easily become familiar 

 with it by the aid of the special drawings scattered among the text figures. 



Although the Tertiary bryozoans often occur literally by the million in a 

 stratum, they are usually so inconspicuous as to be unnoticed by the average 

 collector. When these fossils are present a careful examination of a weathered 

 outcrop will almost invariably reveal a few minute twig-like stems or porous, 

 flattened fragments projecting from the surface. Further search along the outcrop, 

 especially along a seam in the rock, is very liable to result in the discovery of many 

 such fragments. 



As most of the American Tertiary bryozoa occur in soft limestone or marls, 

 the collection of the material for study consists simply in scooping up a large 

 amount of the loose rock containing these fragmentary remains. If the specimens 

 are found in a hard, indurated rock, it is usually only a matter of search to find 

 a >pot where the matrix has decomposed, leaving the soil filled with free specimens. 

 In any case it is not advisable to pick up the specimens one by one, not only on 

 account of loss of time, but also of breakage. On arriving at the laboratory the 

 clay or other rock holding the bryozoans should be allowed to soak in water for 

 some hours. The material may then be agitated and the muddy water poured 

 away. Continuing this process until the agitated water no longer becomes muddy, 

 the residual mass is set aide to dry. The debris when dry is then ready for 

 assorting, although passing it through several sieves of different mesh greatly 

 facilitates the assorting of the contained fossils. 



When bryozoa are quite rare in any exposure it is well to do most of the 

 sieving in the field if possible. For example, the interesting lowest Eocene fauna 

 -i cured at T'pper Marlboro, Maryland. wa> collected only after several days' active 



