162 Forty-sixth Effort on the State Museum. 



some investigation which should deal directly with these ques- . 

 tions. And moreover the science demanded the results of such 

 an investigation in aid of its future progress. 



The original conception and plan of the work which the author 

 had proposed to himself was a very simple one, viz. : to select 

 the earliest representative of a genus in any of the geological 

 formations and to follow it through all its manifestations and 

 modifications in geological time, to its final disappearance ; or so 

 far as these modifications should appear in the Palaeozoic rocks, 

 to which he had limited his research.* With the knowledge 

 then possessed and with the collections at his disposal he had 

 supposed that the result of such an investigation could be 

 embraced in a supplementary part to Yolume lY, and under this 

 title the work was announced. This study was commenced very 

 soon after the publication of that volume and its general plan 

 was carried out so far as the lithographing of about thirty plates, 

 when the farther progress of the work was suspended, to be 

 resumed only in the latter part of 1888. 



In the meantime the duties of the author had separated him 

 almost entirely from this work, and owing to changes, over 

 which he had no control, in the organization and management of 

 the State Museum, the collections which he had planned to make 

 for use in its preparation had not been made. The progress in 

 our current knowledge of the subject, and that recorded in the 

 publication of volumes and miscellaneous papers during more 

 than twenty years had been enormous, and the undertaking which 

 had been deemed feasible in 1867, seemed almost beyond attain- 

 ment in 1888. The work was resumed however, with no other 

 collections immediately available for use, than those upon which 

 it had been commenced. In the original plan four plates were 

 left for the illustration of the Inarticulata ; the present volume 

 furnishes ten additional plates, and the illustration of these forms 

 may be regarded as fairly complete, according to our present 

 knowledge. 



The plates which were lithographed at the commencement of 

 the work are designated on the upper left-hand margin as 



* The difficulty of procuring sufficiently abundant and characteristic collections of the later 

 formations was in itself a sufficient barrier, and the scope of the work did not contemplate the 

 discussion of Mesozoic and later genera, except in an incidental manner. 



