96 



Contributions to Palaeontology. 



the condition is essentially the same. Everywhere frag- 

 mentary, 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 con- 

 nection, and these so badly crushed as to be of no use for 

 illustration. The material consists of glabellse, separated 

 cheeks, caudal shields, and fragments of thoracic articu- 

 lations, 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, as far as known, are restricted to a single locality. 



I have not been able to make out, with certain t} r , 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 Dikelocepha- 

 lus of Owen as Conocephalites, 1 I find the former in 



1 This has already been done by Dr. B. F. Shumakd in bis paper cited, and 

 I have, therefore, thelesshesitancy in publishing this opinion. The personal 

 and traditional knowledge of the originals of Dr. Owen's species, possessed 

 by Dr. Shumard, renders his remarks of peculiar interest and value. 



