46 U.S. NATIONAL MUSEUM BULLETIN 255 



for the North American Lepidoptera that "the farther north samples 

 were collected the higher both the frequency of melanic forms per 

 species became and the nmnber of species exhibiting melanism." In 

 this regard, T. m. extranea is further interesting in that its kno-wTi dis- 

 tribution is apparently more southern than that of the nominal sub- 

 species (see map 4). Unfortunately, other than general locality, 

 relatively little is known of the precise origins for the moths examined 

 in the present study. Considerably more localities need to be sampled, 

 and close attention should be directed toward the gathering of altitu- 

 dinal data. The latter is particularly important in such a topographi- 

 cally diverse region as the State of California. 



As a result of his studies on geographical melanism, Kettlewell 

 (1961b) further separated the insects exhibiting this phenomenon into 

 three groups : 



1. Species in which 100 percent of their population is melanic; 

 they have discarded their normal alleles found elsewhere. 



2. Species in which the two forms co-exist as a balanced poly- 

 morphism. 



3. Species in which there is found an indefinite range of forms 

 from black to pale; these presumably reflect either a multifactorial 

 situation, or one in which variable heterozygotes occur. 



It is apparent that T. m. extranea represents an example of the 

 first group. This supposition is based upon the uniform color and 

 relatively distinct size of the subspecies, as weU as its distribution. 

 Eighty specimens of T. m. extranea and 105 of T. m. maculata were 

 examined m. the course of this study. Only one individual, a specimen 

 of T. m. extranea, showed any evidence of intermediacy. The color 

 of that specimen is entirely black except for the head and collar, which 

 are dusky white. The moth probably represents either a hybrid of 

 the two subspecies, or else a rather unusual variation of T. m. extranea. 



Perhaps of more significance than color in separating the two 

 subspecies of T. maculata is that of size. Consistent differences in 

 size as well as in distribution suggest a greater genetic difference than 

 does color, which in some melanic forms may be under relatively 

 simple genetic control (Ford, 1953). The lengths of the forewings 

 of 30 females were measured for both subspecies (see tabulation below), 

 and the differences were found to be significant (P=^0.02 and 

 <0.03). A similar size difference has been noted in a British noctuid, 

 Diarsia jestiva SchiffermiiUer (KettleweU, 1961b). The melanic 

 subspecies of this moth is distinguished from the typical form in being 

 smaller as well as much darker. This species, however, demonstrates 

 the normal distributional pattern of most melanic Lepidoptera 

 (geographical type) in that the darker subspecies, Diarsia jestiva 



