56 CLARK — THIRTY-THREE NEW SPHINGIDAE ['vol'.^li?' 



"3. Note, excelsior has two forms of larva, my published form 

 resembling leachi, but another, since found, resembling zebra, 

 but the narrow belts on a black ground are always distinctly 

 lemon-yellow, and do not reach the red claspers. The long black 

 tail of excelsior is undoubtedly the longest of the whole genus, 

 as yet known. 



"4. My experience of the larva in the pattern, color, habits, 

 and habitats, would seem to show that scyron and allamandae, 

 also menechus and mossi, are further removed in the same genus 

 from all four forms which I have mentioned. The resemblance ' 

 in the moth of scyron is, I am convinced, superficial rather than 

 real. 



"5. The very select and fastidious habits of zebra, very rare 

 in Para evidently, and only occasionally to be found on the 

 tender-leaved Succubas growing in the heavy shade of giant 

 forest trees, in itself indicates that it is a distinct species from 

 I. swainsoni, which latter was always found by me in Perene 

 and Chanchamaj'o on the Succubas growing in bush form on 

 the hillsides in bright sunshine, surely an important considera- 

 tion which can hardly be regarded as a subspecific feature. 



"All this should be taken into account and remembered, 

 whatever else may subsequently be determined by the examina- 

 tion of the various imagines and their genitalia. Be careful, 

 therefore, in your descriptions to note that, from the larva 

 zebra is near to tetrio, nearest to swainsoni, near to leachi, equally 

 near to excelsior (generally an Amorpha feeder) but far from 

 scyron (invariably and only on Allamanda). This genus Isog- 

 nathus constitutes a highly important biological study." 



Coming to a description of the adult insect, the relative em- 

 phasis which should be given to differences in the imagos of the 

 Sphingidae, and to differences in the juvenal stages, is one of 

 those things upon which much may be said. There is no doubt 

 that in its general facies Isognathus zebra is closer to I. scyron 

 Cr. than to any other form. As I compare my pair of I. zebra 

 with a long series of I. scyron, differences are hard to detect. 



The male of I. zebra has, basally of the dark postmedian 

 longitudinal area between R3 and Ml, three heavy dark lines, 



