REVIEWS 83 
the most remarkable illustration of all is to be seen in Professor Hyatt’s 
new Classification of Cephalopods. The chapters on Nautiloids and 
Ammonites, occupying 75 pages, have been entirely rewritten by Pro- 
fessor Hyatt, and represent in epitome a life work expended on the 
study of these groups. The system followed was proposed in outline 
at the Boston meeting of the American Association, two years ago. 
Its essential feature consists in the elevation of the three leading 
“genera”? of von Buch, Gonzatites, Ceratites, and Ammonites, together 
with the Clymenoids of Giimbel, into as many different suborders, 
and in addition to these, several entirely new ones are recognized 
among the Goniatites and Ammonites. A large number of genera are 
made the types of independent families, and the prevailing feature 
throughout is the comparison of young stages of specialized forms 
with the adult of primitive types. As the entire life history of 
Ammonites and other groups are recorded in the progressive changes 
taking place in the shell, this class of organisms is especially well 
suited for comparative investigations based on the principle of accel- 
lerated development. 
The chapter on Trilobites is from the pen of Professor C. E. Beecher, 
our leading authority on this group. The treatment is much fuller 
than in the original, and a considerable number of new figures are 
added. As inthe Ammonites it is of prime importance to compare the 
ontogenetic stages, and this furnishes the key to the new classification of 
Beecher, since adopted by Cowper, Reed, Bernard, and others, although 
opposed by Pompeckj. ‘Trilobites are here accorded the rank of a 
separate subclass, all other crustacean forms being set off against them 
under the title of Eucrustacea. The latter have been revised for the 
present work by Professors J. M. Clarke and J. S. Kingsley, with the 
exception of the Ostracoda, which are accredited to Mr. E. O. Ulrich. 
A noteworthy point consists in the removal from Crustacea of the 
Merostomata, including Limulus, the Eurypterids, etc., and associat- 
ing them with the Arachnids under the head of the Acerara, of Kings- 
ley. This step, it is believed, will eventually be acquiesced in by most 
specialists on these groups. Altogether, the chapters on Arthropods 
show evidence of most careful revision, and are well-balanced as 
regards space. 
We come lastly to the chapters on Arachnids, Myriopods, and 
Insects, which have been revised and slighly enlarged by that inde- 
fatigable paleoentomologist, Professor S. H. Scudder. Save for being 
