182 PROCEEDINGS OF THE NATIONAL MUSEUM vol. los 



attention. In addition, however, it has been possible to devote some 

 attention to the secondary considerations such as variabiHty, geo- 

 graphic distribution, and relative taxonomic status of the various 

 forms. 



In addition to establishing a degree of stability in the genus, and 

 providing a means for other workers to identify their specimens with 

 confidence, the present paper may serve another purpose, that of 

 emphasizing the desirability that such studies might become the rule 

 rather than the exception. It is a matter of regret that most of the 

 work still being done on diplopods consists merely of brief descriptions 

 of miscellaneous new forms, with little or no attempt at integration 

 with existing facts. This approach is in no way different from, much 

 less superior to, the work of the catalogers of the early 19th century, 

 and serves only the isolated purpose of providing names for taxo- 

 nomic entities with as little consideration as possible. Furthermore, 

 it contributes nothing to the general knowledge of evolution in the 

 Diplopoda, it confuses an already difficult situation (particularly from 

 the standpoint of the beginner), and produces a volume of unrelated 

 facts which must eventually be assembled, evaluated, and reorganized 

 before they acquire any significance. By contrast, the treatment of 

 entire genera with some concern for thoroughness requires only 

 slightly more labor, and the result is undeniably more attractive and 

 useful for all concerned. 



For the preceding reasons, plus the fact that material of most of 

 the named forms was at hand or readily available, I was prompted 

 several years ago to undertake a revision of Pachydesmus, which is 

 now offered to mj colleagues and successors with the belief that I am 

 leaving the genus in somewhat better condition than I found it. 



Materials and Methods 



During the preparation of this paper, I have examined a total of 68 

 specimens of Pachydesmus, representing all of the forms considered to 

 be valid. This material is contained in seven collections, which are 

 listed, with the abbreviations used for their designation, as follows: 



AMNH: American Museum of Natural History, New York, N. Y. 



CNHM: Chicago Natural History Museum, Chicago, HI. 



MCZ: Museum of Comparative Zoology, Cambridge, Mass. 



NBC: Private collection of Nell B. Causey, Fayetteville, Ark. 



RLH: Private collection of R. L. Hoffman, Blacksburg, Va. 



RVC: Private collection of Dr. R. V. Chamberlin, Salt Lake City, Utah. 



USNM: U. S. National Museum, Washington, D. C. 



In many instances, it happens that the value of a systematic paper 

 is directly proportional to the number of type specimens examined by 

 the author. This is particularly true in the case of diplopods, espe- 

 cially when the original description included inadequate illustrations 



