Variations in Pronuba and Prodoxus. 51 



Prodoxidse. The black 'form of Pronuba maculata presents us 

 with the question of varietal or specific value that has arisen 

 with the plant itself upon which it occurs, so far as regards the 

 variety graininifolia of Yucca whipplei Most specialists would 

 be inclined, without any intermediate specimens, to charac- 

 terize this black form as a distinct species, especially as it is 

 dissociated from the other more typical forms and confined to 

 one particular variety of Yucca. Yet in every other character 

 but color it agrees precisely with the typical maculata, and I am 

 strengthened in my view of considering it a mere variety by the 

 well-known variation in the maculation of the typical species. 

 It is a form that is differentiated as to color without having yet 

 acquired any essential structural differences, though it may 

 have lost the power to intercross with the typical form. Here, 

 also, the color must be looked upon as of secondary importance 

 to the species, and more or less fortuitous, as it is difficult to see 

 what advantage the purely black has over the maculate form, 

 especially in an insect essentially diurnal. 



So it is in the variation of the banded species of Prodoxus. 

 Some of the specimens combine the characters of at least two 

 different species, without being referable to either, satisfactorily, 

 and in the present state of our knowledge most entomologists 

 would be justified in describing them as distinct species; but 

 there can be little doubt that, when abundant material from dif- 

 ferent localities. is obtained, all these transversely-marked forms 

 will be difficult to separate. Such, however, is the case in almost 

 every genus, whether of. plants or animals, and the Prodoxids 

 simply furnish us with a rather marked illustration of the fact 

 that the variation has gone on and is going on, so far as purely 

 colorational characters are concerned, without any very definite 

 and unchangeable differences having yet been acquired. How 

 strikingly such facts compare with the permanency, even in col- 

 orational characters, of such well-established species in the same 

 order as the cosmopolitan Vanessa cardui, which, with a most 

 beautiful wing design and a most complex colorational pattern 

 on the inferior surfaces, remains essentially constant in all its 

 details in all parts of the world where it is known. 



The decurved hooks in the larva of Prodoxus cinereas are also 

 most interesting from an evolutional point of view. Such anal 

 hooks are extremely rare in Lepidopterous larvae, being found in 



