198 
AERIAL AND TERRESTRIAL DIPTERA 
described by Walker as an Asilid, and Westwood, who drew the 
figure (in the “ Insecta Saundersiana ”), evidently shared this error. 
Lampromyia Macq., a Leptid, was redescribed by Perris as a new 
genus of Asilidae, Apogon. The genus Leptynoma Westwood 
(from the Cape), described by him as an Asilid, is either the same 
as, or closely allied to, the Leptid Lampromyia Macq. 
I have compared the LJremochaeta with the Marsupialia among the 
Vertebrates. The Marsupialia contain animals foreshadowing in 
their general appearance more recent forms. The above-mentioned 
group of genera of Leptidae , mimicking Asilidae, seem to represent 
an analogous case, and a further study of the remarkable super¬ 
family Eremochaeta may disclose still other resemblances of the 
same kind. 
Another very interesting instance of the juxtaposition in the same 
group of two opposite types of life-habit is likewise found among 
the Leptidae , in the genera Coenomyia and Xylophagus. Although 
the imagos show important differences in the head, antennae, scu- 
tellum, venation, etc., the comparison of the larvae proves that the 
two genera are very closely related, and do not belong to two dif¬ 
ferent families, as was formerly believed (by Schiner, “ Fauna,” Vol. 
I, p. 26, and by myself, in “ Catalogue of North American Diptera,” 
1878; Loew placed them in the same family, but with a doubt, 
“Monographs North American Diptera,” Vol. I, p. 16, 1862). 
Coenomyia is holoptic in the male, Xylophagus distinctly dichoptic in 
both sexes, and, in agreement with these characters, Coenomyia has 
more aerial habits and flies better than the pedestrian Xylophagus 
(Schiner, loc. cit., says of the latter: “ finden sicli an Baumstam- 
men . . . wo sie munter auf und ab rennen”). In Europe, 
there are no transitions between these two genera, but in North 
America, with its older fauna, the interval between Xylophagus 
and Coenomyia is filled up by the genus Arthropeas Loew, and 
several allied genera. 
The case of Xylophagus and Coenomyia reminds me of the two species of the 
coniferous tree Sequoia in California, S. sempervirens and S. gigantea, the former 
occurring along the seashore, the other high up in the mountains. Prof. Oswald 
Heer of Zurich, the great student of fossil plants, enumerated twenty-four fossil 
Sequoiae, occurring in Tertiary and Cretaceous strata and spread over Europe, Asia, 
and North America, as far north as Spitzbergen (78° of latitude), and as far south as 
