Recent Literature. 
235 
what he has here to offer, we are at length presented with the complete 
result of his patient and faithful investigations, together with the final 
conclusions deduced from his study of these marvellous forms of bird life. 
It is safe to say, that no single memoir on fossil birds hitherto published 
can be compared with this in accuracy of detail, in importance of the 
material upon which it is based, in beauty of illustration, and in value of 
results attained. 
Remains of Mesozoic Birds hitherto brought to light have been for the 
most part too fragmentary and too few to throw much light on the orni- 
thology of that period. Excepting the well-preserved remains of three 
individuals of the Jurassic Archaeopteryx, the only other Mesozoic Birds of 
the Old World are from the Cretaceous of England. The present volume 
is based on the remains of more than one hundred different individuals of 
the Odontornithes procured in the Cretaceous deposits of the West during 
the last ten years. The extent of such remarkably well preserved ma- 
terial is wholly unparalleled. Since the first fossil bird was discovered by 
Prof. Marsh, in December, 1870, near the Smoky Hill River in Western 
Kansas, in middle Cretaceous strata, corresponding to those named by 
him the “ Pteranodon beds,” these deposits have yielded nine genera 
and twenty species, represented by the remains of about one hundred and 
fifty individuals. Says Professor Marsh, in his Introduction : — 
“ A study of this extensive series of Bird remains brings to light the 
existence in this class of two widely separated types, which lived together 
during the Cretaceous period, in the same region, and yet differed more 
from each other than do any two recent birds. Both of these types possessed 
teeth, a character hitherto unknown in the class of Birds, and hence they 
have been placed by the writer in a separate sub-class, the Odontornithes. 
One of these groups includes very large swimming birds, without wings, 
and with the teeth in grooves ( Odontolcce ), and is represented by the genus 
Hesperornis. The other contains small birds, endowed with great powers 
of flight, and having teeth in sockets (Odontotormce) , and biconcave verte- 
brae ; a type best illustrated by the genus Ichthyornis. Other characters, 
scarcely less important, appear in each group, and we have thus a vivid 
picture of two primitive forms of bird structure, as unexpected as they 
are suggestive.” 
These two groups, Odontolcce and Odontotormce, Professor Marsh com- 
pares with the Jurassic Saururce of Haeckel, making of the three as many 
orders of his sub-class Odontornithes. Their characters are contrasted on 
page 187, and it is interesting to observe, in the tabulation of their charac- 
ters, how much better known are the Odontolcce and Odontotormce than the 
much longer known Saururce. 
The work of Professor Marsh, as a whole, is an unmeasured advance 
upon all previously obtained knowledge of Cretaceous birds. 
The present volume is divided into two parts, the first treating of Hes- 
perornis , the second of Ichthyornis and Apatornis , the entire skeletons of 
