30 FOSSIL TURTLES OF NORTH AMERICA. 
elongated reptiles, in the skulls of which there were many chelonian characteristics 
and whose bodies were protected by an armor of elongated plates overlying the ribs. 
The stegocephalian genus Archegosaurus, of the Permian, possest a ventral armor 
of elongated plates. We may confidently expect that in the Permian there will yet 
be found an animal possessing such a combination of these characters, together 
with other features, that we can recognize in it the ancestor of the order of turtles. 
As to the relationships of the turtles to the orders of reptiles, other than the 
Cotylosauria, only a few words can be said. The opinion is generally maintained 
that their relationships are closer to the Plesiosauria than to any other order. Baur 
(Jour. Morphology, 1, 1887, p. 98) has enumerated a number of resemblances 
between the two groups. Among other things, he states that the pelvic arch of the 
Nothosauride, among the most primitive of the Plesiosauria, is only comparable 
with that of the Testudinata. It may be remarked that the pubes in both the turtles 
and the plesiosaurs are greatly expanded forward and laterally. The ischia are not 
so much alike, those of “the plesiosaurs being much more extended backward than 
those of the turtles. Baur says that in the humerus of the lower Plesiosauria there 
is an ectepicondylar foramen; but, according to Furbringer, there is only an 
entepicondylar foramen. Baur does not compare the skulls of the two orders. The 
strongest argument in favor of the relationships of the two orders is found in sup- 
osed resemblances in the shoulder-girdles. Probably the best presentation of this 
is to be found in Fiirbringer’s elaborate paper in the Jenaische Zeitschrift, Xxx1v, 
1900, page 326. In that treatise the author takes the ground that the process 
directed interiorly and inwardly from the scapula in the turtles is a procoracoid, a 
view adopted by the present writer. Fiirbringer also holds that the procoracoid 
was present in the Plesiosauria. This opinion ihe been accepted by some authors 
and disputed by others. To the present writer the tract of bone in question appears 
to be simply an extension forward and mesially of the scapula, whether that 
extension is regarded as an acromion or a “ventral ramus” of the scapula. The 
tract advanct gradually from the scapula to the midline, and there is no evidence 
that it ever was a distinct bone. The fact that the two clavicles do not lie between 
the ends of these processes does not appear to be decisive, for in numerous reptiles 
the clavicles extend laterally on the scapula. Opposed to the idea that there are any 
special relationships between the turtles and the plesiosaurs are the facts that the 
latter always possess large supratemporal fenestra, the former never; and that the 
most primitive plesiosaur, Lartosaurus, has the digital formula belonging to the 
Diapsida and not that of the Synapsida. 
At best, the relationship between the turtles and the plesiosaurs is not close; 
and the most that we can say 1s that possibly the cotylosaurian stocks of the two 
orders were a little closer to each other than to stocks that gave rise to the other orders. 
THE GEOGRAPHICAL DISTRIBUTION OF LIVING TURTLES. 
At the present day turtles exist in all the larger divisions of the earth, wherever 
there is sufficient heat, at least a moderate amount of moisture, and a supply of food. 
They occupy too all the warmer seas. Fig. 9 is an outline map that includes all the 
lands and seas in which these reptiles are found: The areas occupied by the land and 
fresh-water forms are indicated by parallel rulings, except that certain small islands 
are made black; but no attempt has been made to show the distribution of the marine 
species. Their realm may be taken as comprising all the seas between the ruled areas. 
This map and those succeeding i it have been compiled with considerable care; but 
itis not possible in all cases to determine exactly the limits of the groups. 
