1863.] MR. H, W. BATES ON BUTTERFLIES FROM PANAMA. 247 



and were the species in every genus so neatly arranged and circum- 

 scribed in nature as they are in the monographs of naturahsts, the 

 conclusion arrived at by most students, namely that they were all 

 independently created, would be certainly the only one that could be 

 drawn. It would be desirable to know whether none of these in- 

 structive species occur in ornithology and in the other branches of 

 zoology. 



18. Mechanitis isthmia, n. sp. PI, XXIX. fig. 1. 



Expanse 2" 7'". Fore wing, above, brownish black, a basal streak 

 over the median nervure and the hind margin being orange-tawny ; 

 a spot across the cell near its termination, an interrupted belt across 

 the wing from the costa to near the middle of the outer margin, and 

 an oblong subapical spot yellow. Beneath, the same, except that the 

 hind angle is also orange-tawny, and that there is a row of eight 

 submarginal white spots along the outer margin. 



Hind wing, above, orange-tawny, with a spot near the apex and a 

 narrow outer border from the middle of the costa to the anal angle 

 brownish black. Beneath, the same, except that the root of the wing 

 has a yellow spot, and that there is a submarginal row of five white 

 spots. 



Body brownish ; wing-lappets and thorax spotted with tavray- 

 orange ; antennae yellow, with the base dusky. 



This is one of the numerous local forms of Mechanitis polymnia, 

 a species which exhibits the process of variation, segregation of local 

 varieties, and formation of species in the same way as already de- 

 scribed under /. ninonia. But the proof of complete formation of a 

 species is more complete here than in the last, seeing that one at 

 least of the local forms^ — proved by the existing variability of the 

 species in other districts to have been derived from the same stock — 

 coexists with a sister form without interbreeding with it. The vari- 

 ous races and half-formed races of Mechanitis polymnia are distri- 

 buted each in its district over the whole of Tropical America ; the 

 two sister races which coexist in the manner described are M. po- 

 lymnia, var. lysimnia and var. nescea, in the neighbourhood of Bahia 

 in South Brazil. 



19. Heliconius hecalesia, Hewitson. 

 Ueliconia hecalesia, Hewits. Exot. Butt. Hel. f. 6. 



This most beautiful and distinct species, like Tithorea tarricina, 

 has hitherto been recorded only as inhabiting New Granada. Like 

 T. tarricina also, the Panama example differs in a slight degree from 

 the New Granada type, the yellow submarginal spots of the hind 

 wings being much smaller. 



20. Heliconius demophoon, Mdnetri^s. 



Heliconia demophoon, Men^tr. Cat. d. 1. Coll. Imp. Ac. des Sci. 

 gt. Petersbourg, p. 86, t. 2. f. 4. 



This handsome species occurs also in Nicaragua and Mexico. It 



