PREFACE. 



The present bulletin on the Mesozoic Echinodermata of the United 

 States is the first of a series of reports on American fossil radiates. 

 The material for a review of the Cenozoie Echinodermata has already 

 been collected, and the results of that work will be shortly added. 



The investigation of the Mesozoic Echinodermata, first undertaken at 

 the request of Dr. (J. A. White, was intended to include only the material 

 in "the i)ossession of the U. S. National Museum, but the necessity for 

 wider comparisons aud a general treatment of American species became 

 apparent as the work advanced. The larger collections in other in- 

 stitutions Avere accordingly drawn upon, and as a result the number of 

 new forms has been greatly increased, while misconceptions that have 

 hitherto existed as to the limitations of many of the earlier species have 

 been rectified. 



Much i)oor material that indicates other and new species has been 

 ignored in this review, so that further collections will doubtless largely 

 increase the number of American forms. 



The writer is under great indebtedness to Prof. Robert T. Hill for in- 

 formation in regard to the geological range and localities of manj- of the 

 Texan species and for the loan of a large amount of material. Further, 

 the writer desires to extend his thanks to Prof. Angelo Heilpriu, of the 

 Academy of Natural Sciences of Philadelphia, Prof. K. P. Whitfield, of 

 the American Museum of Natural History, New York, Prof. Alpheus 

 Hyatt, of Boston, Prof. O. C. Marsh, of Ncav Haven, Mr. (I. WolfHol- 

 stein, of Texas, I)r. G. Hambach, of St. Louis, Prof. Samuel Calvin, of 

 the University of Iowa, Mr. E. T. Dumble, State Geologist of Texas, 

 Mr. E. J. Pond, of Washington, ^Ir. F. A. Sampson, of Sedalia, Missouri, 

 and others, for the opportunity to use the important collections in their 

 possession. 



The writer is under the greatest obligations to Mr. C. R. Keyes, who 

 has executed the very complete and accurate scries of structural draw- 

 ings, aud whose extensive knowledge of the Echinodermata gives to the 

 other illustrations prepared by him an especial value for determinative 

 purposes. The author is also indebted to Mr. H. C. Huutcrfor the care 

 he has shown in the preparation of the drawings intrusted to him. 



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