228 
1863.] 
nest, ^jastly, it is well known that there are three distinct types of 
the Lepidopterous Vanesm interrogationis, which were “all obtained from 
the same caterpillars” by Boisduval & Leconte. (Quoted by Mr. Ed¬ 
wards, Proc. Ent. Soc. Phil. 7, p. 184.)—In the meantime, the general 
non-existence of intermediate grades between two closely-allied forms 
may and must be taken as prima facie evidence of their specific dis¬ 
tinctness. That “ the exception proves the rule” is an old and not 
very philosophical saying; but that there are exceptions to almost all 
rules in Natural History is undoubtedly true. Monomorphism is the 
rule; Dimorphism is the exception. 
It may be observed here that in many, though by no means in all, 
Odonatous groups there is a great overplus of 'S 'S . In the same way 
Mr. Edwards has remarked to me that in the genus Papilio the % % 
are about four times as numerous as 9 9 , and I can confirm the fact 
from my own observation. I shall afterwards prove that this is also 
the case in a subgroup of the subgenus Gromphus* In the two subge¬ 
nera of Hetasrina (Lais and Hetaerina) it appears to be almost the 
universal rule. Of the 37 described species of these two closely-allied 
subgenera, although collectors of course always strive to make up pairs 
of each species, the number of S specimens known to exist is about 
366, and the number of 9 specimens known to exist only about 90, 
calculating from my own species and from those where the numbers 
of S 9 specimens are given in the Monogi^aphie; and in no less than 
6 species of the 37 the % only is known. Hence we may conclude that 
generally in the genus Het^rina the S % are at least 4 times as nume¬ 
rous as 9 9 • This great preponderance of 'S S , wherever it exists, 
must give much greater latitude to the above-mentioned kind of “ natu¬ 
ral selection,” than if the sexes were equal in number or 9 9 more 
numerous than S % . 
H. pseudamericana n. sp. % . Brassy-black. Top of the head, including the or¬ 
bits of the eyes, coppery-red, occasionally greenish-brassy. Epistoraa generally 
greenish-brassy, sometimes coppery-red when the top of the head is also so, al¬ 
ways with a lateral whitish spot; rhinarium blackish; labrum very pale dull 
brown, with a large, shining, basal, black spot in the middle; labium and its 
lobes brownish white; mandibles whitish on their basal shining black on their 
terminal i. Back of the head blackish; postoccipital tubercles obtuse. Antennse 
black, the 2nd joint whitish at base and tip, sometimes entirely whitish except 
a small medial black spot. Prothorax dull coppery-red. Dorsum of thorax cop¬ 
pery-red, the dorsal carina black and generally crowned by a faint longitudi- 
