NOTE. 



The letterpress of this memoir was published in an edition of fifty copies, 

 Nov. 26, 1875. The principal edition will appear in the Journal of the Academy 

 of Natural Sciences of Philadelphia, which has not yet been issued, in consequence 

 of the delay in the completion of the plates. These are now published, completing 

 the separate memoir. 



March 20th, 1877. 



