REVISION MALACOSOMA HUBNER IN NORTH AMERICA 35 



females have been examined for morphological difTerences between 

 species, subspecies, and local populations and, with the exception 

 of those structures discussed below, all species are essentially the same. 

 Of course, this does not mean that differences do not exist which might 

 be uncovered by a inore intensive examination than was performed 

 here. Even if differences of some kind are found, hovv'ever, it still must 

 be demonstrated whether they are indicators of species, subspecies, 

 or even of local populations. 



The chi-omosome number was checked for all species and subspecies 

 except A/, tigris and M. incurvum by making squashes of the testes of 

 mature larvae. The haploid number was 3 1 in every case, and there is 

 no reason to believe it would be different for tigris or incurvum, since 

 the other American and both Palearctic species of Malacosoma {castren- 

 sis and neustrium) which have been examined to date have a haploid 

 number of 31 (Makimo, 1951). 



The only structures that have proved to be of value in separating 

 species are the male and female terminalia, the epiphysis, and, to a 

 limited extent, the color pattern. The terminalia are by far the most 

 useful and reliable. The epiphysis has limited usefulness, but is quite 

 reliable for one species {M. disstria) The color pattern is useful, but an 

 experienced eye often is necessary, and this must be supplemented 

 whenever possible by genitalic confirmation of doubtful cases. 



In this revision the evidence gathered from the examination of the 

 various populations in the field has been given overriding priority. 

 Certainly this is as it should be since the presence of (or lack of) evidence 

 indicating reproductive isolation under field conditions is the most 

 important evidence that can be obtained. In many cases morphology 

 is a very good indicator of relationships, but it often does not reveal 

 the whole story. The results of this study have shown that morphology 

 gives a good indication of some relationships in Alalacosoma, but that 

 a much better overall picture of relationships is obtained when field 

 data are available. Since preserved specimens, however, rarely have 

 any useful field data accompanying them, morphology must be re- 

 sorted to for identification in most cases. 



As is the case with many Lepidoptera, Malacosoma adults are most 

 often identified to genus by their general appearance. Doubtful speci- 

 mens can be confirmed as Malacosoma by examination of the wing 

 venation or genitalia. The overall size and shape of the wings coupled 

 with the two oblique lines (usually slightly bowed outward) on the 

 upper surface of each forewing is quite characteristic for all species 

 (see figs. 119-329). Rarely the lines may be faint or even absent as 

 in figures 213 and 214. 



