CONTRIBUTIONS TO INVERTEBRATE PALEONTOLOGY NO. 4: FOS- 
SILS OF THE LARAMIE GROUP. 
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The illustrations which accompany this article, on plates No. 20 to No 
30, inclusive, have from time to time been prepared to accompany a pro- 
posed monograph of the Laramie Group and its Invertebrate Fauna. A 
large amount of materials and the results of extended observations had 
been collected towards such a monograph up to the time that the field- 
work of this survey was discontinued, but the original plan of publica- 
tion of these results has been abandoned because extended field investi- 
gations and large collections would be necessary to the completion of 
such a work upoh a plan commensurate with its importance. The dis- 
continuance of this survey having made it necessary to abandon the 
original plan, the material now accumulated is published in this article 
as one of the series of Contributions to Invertebrate Paleontology. 
The Laramie Group and its invertebrate fossils have been frequently 
discussed by me in certain of the publications of this Survey during the 
past four years; and as there is some want of harmony in relation to 
some of the views expressed, or of inferences that may be drawn from 
statements made, or from methods of treating the subject in those pub- 
lished articles and reports, those publications may be taken to indicate 
the progress of our knowledge concerning the subject discussed. This 
was necessarily the case, because the field is so large and because the 
subject embraced the investigation of a great group of strata which has 
no known equivalent in other parts of the world. While future investiga- 
tions will no doubt. add greatly to our knowledge of the Laramie Group 
land itsinvertebrate fossils, and perhaps considerably modify the views 
at present entertained, the two following-named publications besides 
this one may be taken as containing an exposition of my views at the 
present time: Pages 255-265 of the Annual Report of this Survey for 
1877; and article xxxvi, volume iv of the Bulletin of this Survey. As 
the general subject has been somewhat fully discussed in these two pub- 
lications, the present article will be confined to the following general 
summary, and to the enumeration of the known invertebrate fossils of 
the group, together with the description of those which are illustrated on 
the eleven accompanying plates before designated. 
The geographical limits of the Laramie Group are not yet fully known, 
but strata bearing its characteristic invertebrate fossils have been 
found at various localities within a great area, whose northern limit is 
within the British Possessions, and whose southern limit is not further 
north than southern Utah and northern New Mexico. Its western limit, 
so far as known, may be stated as approximately upon the meridian of 
the Wahsatch range of mountains, but extending as far to the south- 
westward as the southwest corner of Utah, and its eastern limit is far 
out on the great plains, east of the Rocky Mountains, where it is cov- 
ered from view by late formations and the prevailing débris of the 
