1879-1 
Notices of Books. 
491 
mous plants collected by the same naturalist in the above districts. 
Mr. F. M. Endlich’s paper on “ Erosion-produdts in Colorado ” 
would prove a most instructive study for those — and such writers 
exist — who deny that erosion has any share in the formation of 
the earth’s surface. Dr. C. A. White discusses the palaeontology 
of the “ Laramie group,” and Mr. J. A. Allen gives a synony- 
matic list of the American Sciuri , or tree-squirrels. 
The first number of Vol. v. contains much interesting matter. 
Dr. C. V. Riley and Mr. J. Monell contribute a monograph of the 
American Aphididae — a group of inserts of loathsome aspeCt, but 
interesting from their peculiar system of reproduction, and from 
the ravages they commit in the fields and gardens. The first 
annual generation of Schinoneura Americana , the American elm 
Aphis, consisting entirely of females, issues from impregnated 
eggs which have survived the winter, and without sexual inter- 
course produces a second generation like themselves in structure. 
The third generation is winged. The fourth and fifth again are 
wingless, the sixth winged, whilst the seventh consists for the 
first time of individuals of both sexes. Each female deposits a 
single egg, which is not hatched till the ensuing spring. Amongst 
the natural enemies of this species the author enumerates several 
Coleoptera, especially Coccinellidas, two Hemipterous species, and 
even the larva of a moth ( Semasia prunivora ), The misfortune 
is that the enemies of Aphides are, in point of number and 
voracity, utterly inadequate to the task set before them. 
Prof. E. D. Cope discusses the relations of the horizons of 
extinCl Vertebrates of Europe and North America. The author 
points out, as a consequence of the principle of descent, that the 
types of each age have taken their origin from the generalised 
types of preceding ages, there being no descent from the more 
specialised types. Hence in discriminating the subdivisions of 
geological time we have to be guided by the disappearance 
rather than by the appearance of species. He finds that por- 
tions of all the faunae of all the primary divisions of geologic 
time have been recognised on both continents, — that parallels 
requiring general identification of the principal divisions of these 
faunae may be detected, but that exadt identifications of restridled 
divisions may be made in a few instances only. Between the 
tables of extindl animal and vegetable life there is a discrepancy. 
The plant-life of North America reached its present condition 
one epoch earlier than did the higher Vertebrata. Hence either 
the animal-life of North America has lagged behind that of 
Europe, or the flora of America has been in advance of the 
European. The author mentions that the earliest land verte- 
brates had a persistent chorda dorsalis . 
This number further contains papers on the miocene fauna of 
Oregon; on the birds of Dakota; on the fossils of the Jurassic 
trias of south-eastern Idaho and western Wyoming ; on the fos- 
silised forests of the volcanic tertiaries in the Yellowstone 
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