PREFACE. IX 



where such an account can be found. In another place a a brief 

 review of the Isopod structure has already been given. 



It has not been considered worth while to encumber the legends with 

 detailed explanation of many of the figures that have been taken from 

 other authorities; students, however, who desire to learn the signifi- 

 cance of the lettering not given in the illustrations, are referred to the 

 original papers. 



As a final suggestion I would like to say that my object in under- 

 taking this work has been to assist the student in the determination of 

 the forms by giving figures and descriptions of all the species. It is 

 to be hoped, in case of omissions or errors, that leniency will be 

 observed, for the task has not always been eas} v . 



HARRIET RICHARDSON. 



WASHINGTON CITY, November 1, 1905. 



POSTSCRIPT. 



Since this monograph has been printed, and within the last few 

 days, Dr. H. J. Hansen's paper on the Propagation, Structure, and 

 Classification of the Spheeromidpe has been received. 6 With a large 

 amount of material, a comparison of types from various museums all 

 over the world, and a thorough examination of specimens, Doctor Han- 

 sen has arrived at an excellent classification of this group, which has 

 heretofore been in an extreme state of confusion and so recognized by 

 all who have attempted to determine species or to refer them to their 

 proper genera. In Doctor Hansen's paper new genera have been estab- 

 lished and some old ones canceled. The changes which particularly 

 affect the present paper and which I have not been able to make use 

 of in the text, inasmuch as Doctor Hansen's paper was received too 

 late, are as follows: The genus Cassidisca, new genus, must be can- 

 celed as being a sjmonym of Hansen's new genus Cassidinidea; Cili- 

 csea caudata, C. gilliana, C. sculpta, and C. cordata must be referred to 

 Hansen's new genus Paracerceis. The following list shows these rela- 

 tions more exactly : Cassidisca ovalis = Cassidinidea ovalis; Cassidisca 

 lunifrons = Cassidinidea lunifrons; Cilicsea caudata = Paracerceis can- 

 data,' Cilicsea gilliana, Paracerceis gilliana; Cilicsea cordata Para- 

 cerceis cordata; Cilicsea sculpta = Paracerceis sculpta. 



While in New Haven last summer 1 examined the second pleopods 

 of a number of cotypes of Dynamene perforata and found that the 

 males and females of this species were similar, with the exception that 



Contributions to the Natural History of the Isopods, by Harriet Richardson, 

 Proc. U. S. Nat. Mus. XXVII, 1904, pp. 4-17. 



& Quarterly Journal of Microscopical Science, XLIX, Pt. 1. 1905, new ser., pp. 

 69-135. (October number received here November 11.) 



