588 The American Naturalist. [July, 
preservation of existing types of species and genera in all three 
natural worlds is the effect of unknown forces independently 
acting in reproductive cells and organs, as well as in mineral 
atoms and molecules. If we may expect ever to notice the 
formation of a new species under our eyes, this event will not 
depend upon external conditions, but upon a change in the 
nature of protoplasma, or of the chemical structure of a min- 
eral molecule. The author does not doubt that such changes 
are continually going on in nature, but they are too slow and 
subtile to be accessible to our observation. The chief part in 
such changes will always be due to agents or forces peculiar to 
the elementary organs and exerting impulses, by which per- 
manent forms are resulting. 
CONTRIBUTIONS TO COCCIDOLOGY.—II. 
By T. D. A. COCKERELL, MeEsILLA, New Mexico. 
_ No. I appeared in American Natura.ist, Aug., 1895, pp. 
725-732. 
(1). Icerya rileyi Ckll. In September, 1893, I bred a Letilia 
from a larva living on J. rileyi on mesquite at Las 
Cruces, N. M. The Rev. G. D. Hulst informed me that 
it was “ different from coccidivora and from L. ephestiella, a 
good variety at least.” It may, therefore, be as well to 
put its characters on record :— . 
Letilia coccidivora var. hulstii, n. var—Palpi ascend 
ing; fore wings gray, brownish at extreme base and be- 
yond the first band. The first band, at end of basal 
third, double, consisting of a gray line bordered with- 
out by a white band. A wavy band consisting of two 
blackish lines not far from the exterior margin. Hind 
wings shining white; abdomen above whitish, banded 
with gray. It would seem to connect coccidwora with 
ephestiella, and so, perhaps, all are varieties of one. 
(2). Rhizococcus (?) devoniensis Green, Ent. Record, 1896, p. 260. 
I should certainly prefer to call this Eriococcus devonien- 
