CONTRIBUTIONS TO PALAEONTOLOGY. 121 



With the hope of adding to our knowledge of the primordial 

 fauna of the Northwest, I have, with much labor, selected from 

 very extensive collections of trilobitic remains made at intervals 

 from 1850 to 1859, all that appeared to me of sufficient importance 

 to be illustrated. In a friable sandstone with no vestige of the crust 

 remaining, these fossils offer very unsatisfactory material for in- 

 vestigation. It is, however, apparently impossible to obtain better 

 specimens; for in all the localities examined, the condition is 

 essentially the same. Everywhere fragmentary, the fossils have 

 often been drifted together in such numbers as to make it difficult 

 to trace the limits of individual parts. In a single instance only 

 have a few articulations of a thorax of a trilobite been seen in 

 connection, and these so badly crushed as to be of no use for il- 

 lustration. The material consists of glabellse, separated cheeks, 

 caudal shields, and fragments of thoracic articulations either 

 lying separately or crowded together, sometimes forming the 

 principal part of layers one or two inches or more in thickness. 



It must be confessed that working with such material is very 

 unsatisfactory; and it has been only after most diligent search in 

 many localities, that I have yielded to the necessity of determining 

 and illustrating species from fragments such as are here given. 

 These species, however, have not been determined from single 

 fragments. In some instances twenty or fifty examples occur ; and 

 of most of them, five to ten have been studied. Some of the species 

 have a considerable horizontal range ; while others, so far as 

 known, are restricted to a single locality. 



I have not been able to make out, with certainty, the regular 

 occurrence of successive trilobite beds, as given by Dr. Owen; 

 but my means of exploration have not been as extensive as were 

 his. It is clear, however, that there is a succession among the 

 species ; and we shall probably be able to recognize the fact that 

 those forms occurring near the base of the formation do not 

 extend above the middle, while those of the central portions are 

 not found throughout its entire thickness. 



While recognizing some of the species of Dikelocephalus of 

 Owen as Conocephalites,* I find the former in well-characterized 



* This has already been done by Dr. B. Shumard in his paper cited, and I have 

 therefore the less hesitancy in publishing this opinion. The personal and traditional 

 knowledge of the originals of Dr. Owen's species, possessed by Dr. Shumakd, renders 

 his remarks of peculiar interest and value. 



[Senate, No. 115.] 16 



