4 PROCEEDINGS OF THE NATIONAL MUSEUM vol.68 



valuable in stratigraphic work as any group of organisms and 

 because of their minute size they will be as useful in subsurface 

 investigations as the foraminifera, bryozoa, and ostracoda. 



METHODS OF STUDY 



Perhaps in no other group of fossils is delicate preparatory work 

 more necessary than here. In the black shales, in which most cono- 

 donts occur, this preparation is easily carried out, requiring only a 

 steady hand and careful manipulation of tools. It is especially 

 essential that the ends of the teeth or plates be carefully uncovered, 

 for broken specimens or (hose more or less obscured by matrix can 

 not be classified accurately, because fragmentary or exposed parts 

 are often quite alike in otherwise dissimilar species and genera. 

 Thus the main cusp of Prlomodus, Bryantodus^ HibhardelJa^ and 

 several other genera might readily be mistaken for the simple 

 forms of Drepanodus. Several genera have been founded by earlier 

 writers upon fragments of the denticulated bar and it will be im- 

 posible to place these v/ith any degree of finality until entire spec- 

 imens from the same locality and horizon have been studied. 



Conodonts often occur in great numbers in basal sandstones or 

 conglomerates where naturally they are more liable to be broken. 

 Here, however, careful work will bring out many complete examples 

 as is shown by our present studies upon the Hardin sandstone, the 

 basal division of the Mississippian in central Tennessee. Free speci- 

 mens are not always satisfactorily determined because they are 

 more frequently imperfect. Such specimens are most valuable Avlion 

 during the course of preparation they can be freed from the matrix. 

 However, even imperfect, free specimens can be accurately classified 

 when complete examples of the teeth have previously been studied 

 find illustrated. 



After their preparation, the further study of the conodonts is 

 much facilitated by whitening them with ammonium chloride and 

 photographing them at a uniform magnification. By this method 

 the individual specimens are thus made much more available for 

 comparisons. The method of whitening the specimens has been 

 described by the authors before, but for the sake of completeness 

 we again insert a diagram of the apparatus and a few remarks as 

 to the process. 



By blowing through the mouthpiece ;!/, the fumes of hydrochloric 

 acid (HCl) and ammonium hydrate (NH^OH) will unite at the out- 

 lets of the tubes O, and form a white sublimate of ammonium 

 chloride upon any object held at this point. This sublimate can be 

 deposited in such a uniform thin film, varying in color according to 

 its thickness from a light blue to an ivory white, that all the details 



