THE BRYOZOA — BASSLER. 345 



form). The deliquescence of small pieces of this substance, which 

 needs to be handled gingerly with unprotected hands, laid upon the 

 fossil loosens the clay, which is then easily brushed off. Some work- 

 ers accomplish the same result by placing their specimens in a satu- 

 rated solution of Glauber's salts, which, in crystallizing, also loosens 

 the clay. To prevent continued action of the small amount of caustic 

 potash still remaining the specimen must be carefully neutralized 

 by washing in water containing very dilute hydrochloric acid. 



The Paleozoic species usually belong to the so-called stony bryozoa 

 (pi. 1) in which the zoarial fragments are large enough to be readily 

 visible to the collector. In weathered outcrops these fossils occur as 

 twiglike fragments or lace-like fronds, often so numerous that they 

 can be gathered in large quantities. The solid limestone, such as, 

 for example, the well-known Tennessee marble, is often crowded 

 with branching and rounded fragments of stony bryozoa, which can 

 not be broken out of the rock without destroying the form of the 

 zoarium. Fortunately these can be identified by thin sections just 

 as readily as the free specimens. 



Mesozoic and Cenozoic bryozoa occur in unconsolidated sediments 

 more frequently than in the Paleozoic, so that free specimens are 

 very easily obtained. However, although these bryozoans often occur 

 literally by the millions in a stratum, they are usually so inconspicu- 

 ous 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 twiglike 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 (pi. 2). 



As most of the post-Paleozoic bryozoa occur in soft limestone or 

 marls, the collection of the material for study consists simply in scoop- 

 ing 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 spot 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 proc- 

 ess until the agitated water no longer becomes muddy, the residual 

 mass is set aside to dry. The debris when dry is then ready for 

 assorting, although passing it through several sieves of different 

 mesh greatly facilitates the separation 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 



