FROM THE CRETACEOUS FORMATION OF NEBRASKA. 411 



ADDITIONS AND CORRECTIONS. 



SINCE the preceding paper was communicated, we have had an opportunity of examining more extensive 

 collections of specimens from the Nebraska Territory, brought down by Dr. Hayden. Among these are 

 better preserved specimens of several species here described, which enable us to determine their characters 

 with more precision than could be done with our former collections. 



Page 391. Ftrsus CONSTRICTUS. An examination of a larger and better preserved specimen induces us to 

 regard this fossil as belonging to the genus BUCCINUM. 



Page 393. DENTALIUM GRACILIS. Seventh line of description, for " spiral angle " read " apicial angle." 

 Page 394. HELIX LEIDYI. The aperture is ovate, subangular behind. 



Page 396. HAMITES MORTONI. This fossil presents some characters incompatible with the genus Hamites, 

 and may be placed under Ancyloceras, if we adopt the characters of that genus as given by Pictet. In the 

 same manner the Ancyloceras ? Nicolletii will be included under the genus Ancyloceras as defined by Pictet, 

 but not as limited by D'Orbigny. 



Page 401. Last word on the page, for " longer" read " larger." 



NOTE. 



IN the spring of 1853, the writer of this note was induced to provide the means for a collector to visit and 

 explore some portions of the Mauvaises Terres of Nebraska. He was assured that no government expedition 

 would be sent there that year; and being unable to learn that any private expedition was contemplated, he 

 concluded that the field would be unoccupied, and hoped that some new light might be thrown upon these 

 distant regions, which had but just begun to yield their treasures to the geologist and palaeontologist. One of 

 the principal objects of this expedition was the discovery of the fossil flora of this period, so prolific in 

 remains of Mammalia, as well as to determine more clearly the relations between the Cretaceous formations 

 of the Missouri Valley and those of the region especially known as the Mauvaises Terres. 



Circumstances which it is not neccessary to detail here, and over which the writer or the exploring party 

 had no control, frustrated in a great measure the original objects of the expedition. 



The collections made, and facts ascertained, during the short period which the party remained on the 

 ground, have contributed something to our knowledge of the geology of this region ; and the preceding new 

 species from the Cretaceous formation of the Northwest are not without interest. These would have been 

 given to the public at an earlier period, but have been postponed at the especial request of other parties 

 having new species from the same region. These have already been made known, and are cited in the list 

 of published species given on page 405 ; there is, therefore, no longer any reason for delaying the publi- 

 cation of the foregoing species, which, it will be seen, comprise a number equal to all that have before been 

 described from the Cretaceous formation of that country. 



J. H. 



