ECHINI OF THE EASTERN COAST OF THE UNITED STATES. 249 



extent, and they have been based upon features which are here shown to 

 have so little value, that before we can make a satisfactory comparison of 

 the fossil species with those now living, a thorough re-examination of the 

 fossil Echini from our present stand-point is absolutely necessary. 



In order not to duplicate the descriptions of the Echini of the eastern 

 coast given in this part (Part II.), I shall simply refer to them in their proper 

 place in the descriptive portion of the Revision, Part III. The characters of 

 the families will be fully discussed there ; the genera mentioned are, how- 

 ever, described at length, as their limits are frequently so different from those 

 generally accepted that, unless this were done, some confusion would natu- 

 rally follow. In order to illustrate the species of the Report as fully as 

 practicable, several of the Plates of the descriptive and anatomical parts 

 have been issued with the present Report, as it was found impossible to draw 

 the line distinctly between the plates belonging to the different parts of the 

 Revision of the Echini. 



