2 Doll and Bartsch The P \jramidellidw. 



vide the groups sufficiently to make it reasonably clear where a 

 given species belongs in the series. 



In the absence of anatomical characters it has been necessary 

 to fall back in large part on the. form, ornamentation, and pli 

 cations of the pillar, as distinctive characters, even while we 

 admit that between the different sections some intermediate 

 forms may occur. So many names have been applied to mem 

 bers of the group that in most cases it has not been necessary 

 to coin new denominations. The synonymy, which is very in 

 volved, is reserved for another paper in which the species of 

 the west coast of America will be moriographically treated. It 

 was thought best to put on record the classih'cation adopted, so 

 that before the paper referred to appears the authors may have 

 the benefit of criticism from other students. Many of the 

 specific names given in the past have been repeatedly used for 

 different species, rendering it necessary in many cases to give 

 new ones. In all cases the synonymy adopted has been based 

 on researches which have begun with the typical species of the 

 original authors, which in some of the most anciently named 

 forms has involved no little labor. Wherever any doubt ex 

 isted in regard to the characters the specimens have been 

 ground down until the pillar has been made visible over a 

 great part of its extent, and in all cases the characters recorded 

 are the result of microscopic study. Only a few of the many 

 named forms have been inaccessible, as the collection of the U. 

 S. National Museum is remarkably rich in species of this group. 



The senior author thinks it only just to state that by far the 

 greater part of the work is due to his associate, who has for 

 several years given unwearied attention to these minute and 

 difficult objects of study. The facilities of the National Mu 

 seum have been constantly at the disposition of the writers, 

 and most of the types are contained in its collection, though 

 thanks for material lent for study are due to the Academy of 

 Natural Sciences of Philadelphia, the authorities of Amherst 

 College, the Zoological Museum of Copenhagen, and numerous 

 private students to whom a fuller acknowledgment will be made 

 in the monograph already alluded to, which is nearing its com 

 pletion. 



The name Obeliscus appeared in the Museum Calonnianum in 

 1797, without a diagnosis or figure. This work is anonymous, 



