ZOOLOGY. 233 
gidide), I do not regard it as necessarily of ordinal value, but sub- 
ordinate to characters already mentioned, of the posterior regions 
of the cranium, the tarsus, pelvis, etc. The forms of the articular 
extremities of the vertebre have also a subordinate value. 
The affinities of the Orders are most easily expressed in the fol- 
lowing outline scheme : — 
Series I., With two-rib ar- Series II., With one-rib ar- 
ticulations and fixed Intermediate. ticulation and free 
* quadrate. quadrate. 
Ornithosauria Ophidia 
4 
Dinosauria Pythonomorpha 
Crocodilia Testudinata < 
i ae 
Sauropterygia Lacertilia 
\ Pee, 
Anomodontia Rhynchocephalia 
Ichthyopterygia 
A tabular arrangement destroys expression of more than one 
line of affinities, but is most convenient for presentation. of diag- 
noses. The above-named groups possess different degrees of rela- 
tionship to each other, and have been combined into groups by 
authors, which are supposed to represent natural divisions. This 
presents some difficulties as yet, on account of our ignorance of 
the structure in certain orders. They may, however, be provision- 
ally placed as follows: — 
A. Extremities beyond proximal segment not differentiated as to form. 
I. Tubercular and capitular articulations for ribs distinct, on centra. 
Os quadratum immovably articulated to squamosal, ete. No sacrum. Icu- 
THYOPTERYGIA. Including one order, Ichthyopterygia. 
B. Extremities differentiated. 
Il. Tubercular and capitular surfaces united. Os quadratum articulated 
with squamosal and opisthotic by ginglymus. Sacrum very small. Strep- 
TOSTYLICA, with the orders Lacertilia, Pythonomorpha, and Ophidia. 
III. Tubercular and capitular surfaces united. Os quadratum articulated 
with squamosal, opisthotic, etc., by suture. Sacrum small. Synaprosavu- 
RIA, with the orders Rhynchocephalia, Testudinata, and Sauropterygia. 
IV. Tubercularand capitular surfaces separated ; former on diapophysis, 
atter on centrum. Os quadratum articulated by suture with its suspenso- 
rium. Sacrum generally of several vertebra. ARrcHosauRIA; orders, — 
Anomodontia, Dinosauria, Crocodilia, and Ornithosauria. 
A.A,A. 8. VOL. XIX. 380 
