454 PROCEEDINGS OF THE NATIONAL MUSEUM vol. ii4 



exactly correct, for in the caddis flies a weak Neotropical element 

 enters the southwestern United States, and a Nearctic element extends 

 into the highlands of central Mexico and possibly even farther in the 

 mountains of Central America. 



The terms "metamorphotype" and "pharate adult" that will be 

 used in this series of studies are defined as follows: In the pupal stage 

 most caddis flies are enclosed in either a scaled case or a silken cocoon 

 and the sclerites of the last larval instar are retained with the pupa. 

 Just prior to emergence the adult, except for the wings, is fully formed 

 and hardened; hence the genitalia and many other structural characters 

 are available for positive specific determination. Thus with one 

 specimen are to be found the larval sclerites, pupal skin, and adult 

 structures that give absolute proof of the correct association of all 

 stages. Such a specimen was named a metamorphotype by Milne 

 (1938). The adult found in a metamorphotype is here called a 

 pharate adult, a term proposed by Hinton (1946) for a stage which 

 has become free from the cuticle of the preceding instar, although the 

 cuticle has not yet been cast off. 



The material used in this study is from the following sources: The 

 Cornell University (CU) collection, for the loan of which I am grateful 

 to Dr. H. Dietrich and Dr. J. G. Franclemont; the undetermined 

 material in the collection of the Museum of Comparative Zoology 

 (MCZ) at Harvard University, for which I am indebted to Dr. P. J. 

 Darlington, Jr.; a collection made in Ecuador b}^ Dr. R. W. Hodges 

 while on an expedition supported by a National Science Foundation 

 grant to Dr. G. W. Prescott; the holotypes and allotypes of the species 

 described from Dr. Hodges' collection are being deposited in the 

 United States National Museiun; and the collection of the U.S. 

 National Musemn (USNAI). 



Family Rhyacophilidae 



The typical subfamily Rhyacophilinae is absent in the Neotropical 

 region, its place being taken by the Hydrobiosinae. To date, 16 

 hydrobiosine genera have been described from the Neotropical region. 

 Of these genera, Atopsyche Banks is the largest in included species 

 (30 described to date) and occupies the greatest range, from south- 

 western United States to northern Argentina. The southern tip of 

 South America, however, contains a great number of smaller genera, 

 some members of which are found at least as far north as Ecuador. 



Because I have not seen examples of most genera, the following 

 key is based on the published figures of their venation. The male 

 genitalia are often sources of characters supplementary to the ve- 

 national characters. For an explanation of the venational termi- 

 nology used, see Ross (1956, fig. 154). 



