62 TRANSITION SERIES. 
No higher condition of Vertebrata has been 
yet discovered in the transition formation than 
that of fishes, whose history will be reserved for 
a subsequent chapter. 
The MoUusca,* in the transition series, afford 
examples of several families, and many genera, 
which seem at that time to have been universally 
diffused over all parts of the world. Some of 
these, (e.g. the Orthoceratite, Spirifer, and Pro- 
ducta) became extinct at an early period in the 
history of stratification, whilst other genera (as 
the Nautilus and Terebratula) have continued 
through all formations unto the present hour. 
The earliest examples of Articulated animals 
are those afforded by the extinct family of Tri- 
lobites, (see Plates 45 and 46) to the history of 
which we shall devote peculiar consideration 
under the head of Organic Remains. Although 
nearly fifty species of these Trilobites occur in 
strata of the transition period, they appear to 
have become extinct before the commencement 
of the secondary series. 
The Radiated Animals are among the most 
frequent organic remains in the transition strata ; 
they present numerous forms of great beauty, 
from which I shall select the family of Crinoidea, 
* In this great division, Cuvier includes a vast number of 
animals having soft bodies, without any articulated skeleton or 
spinal marrow, such as the Cuttle-fish, and the inhabitants of 
univalve and bivalve shells. 
