216 Thirty-fifth Report otf the State Museum. 



It had been the intention of the author to incorporate that Preliminary 

 Notice in the Twenty-third Annual Report of the State Cabinet of Natural 

 History, with a preparatory Note making due acknowledgments for sources 

 of aid and information, and giving the reason for the appearance of No. 2 in 

 advance of No. 1. This report (23) was, however, not published till 1872.* 

 In the mean time the burning of the State printing establishment destroyed 

 the material in the hands of the printerf (leaving some proof-sheets only in the 

 hands of the author). No effort was afterward made to resume and complete 

 the intended work, and the paper still remains incomplete. 



The Notice No. 2 was first printed because the investigations upon the 

 genera there included were farther advanced; while comparatively little had 

 been done in arranging the groups preceding those described. It had been 

 the intention to follow Notice No. 2 with the early publication of No. 1, but 

 owing to failing health in 1871, which compelled a cessation of work, and 

 finally an entire absence from my duties, the work was not resumed till a later 

 period. In- the mean time the volume V, Part 2 of Palaeontology, including the 

 Gasteropoda, Pteropoda and Cephalopoda, originally intended to follow the 

 Lamellibranchiata, has been published. The publication of the Lamelli- 

 branchiata should have followed this volume directly, but the continued delay 

 in authorizing the publication of the work induced the author in January, 1883, 

 to issue one hundred copies of the plates, long since completed, with a list of 

 the names of the species proposed. This volume has now been before the 

 public for nearly a year. 



Since the publication of Preliminary Notice No. 2, a more critical study of 

 the forms included in the present paper has shown the imperative necessity of 

 a revision and rearrangement of the species in reference to the genera to 

 which they had in many cases heretofore been referred, and to the proposing 

 of several new generic terms which the author believes will facilitate the work 

 of the student in his investigations in this class of fossils. 



In the preparation of the former paper, the author was very efficiently aided 

 by Mr. R. P. Whitfield, then an assistant in the State Museum, to whom he 

 expresses his obligations. In the preparation of the present publication, 

 together with the previous revision of the species in their generic relations to 

 Pectenidse, Aviculidse, etc., he has been indebted for the very valuable assist- 

 ance of Mr. C. E. Beecher, now an assistant in the State Museum. 



At the present writing, the volume of the text on the Lamellibranchiata is in 

 press and the printing is essentially completed. 



The following Preliminary Notice No. 1 of the Lamellibranchiate shells of 

 the Upper Helderberg, Hamilton and Chemung groups was originally 

 communicated with the Thirty-fourth Report of the State Museum, at the be- 

 ginning of 1881, and should have been printed during that year. This, 

 together with several other papers which were communicated with the 

 Thirty-third and Thirty-fourth Reports, were not printed in the published 

 documents, and were afterward withdrawn and again communicated with 

 the Thirty-fifth Report, of which this paper forms a part. 



Albany, January, 1884. 



* 1873 on title page is an error of the printer. 



t See Twenty-third Report on the State Cabinet Museum, page 249, 1872. 



