54 M. G. MEHL 
THE RIBS ~ 
Of the ribs preserved none resembles the comparatively short, 
straight, distally expanded form figured by Douthitt* in the neck 
region of his skeletal restoration, and commonly found in the large 
collections of Diplocaulus material. It is entirely possible that 
none of the typical anterior ribs were preserved. ‘Those present 
were in a more or less connected pile and not directly articulated 
with the vertebrae. It is assumed, however, that they belong 
near the anterior end of the preserved string of vertebrae where 
they were found, and represent a more primitive stage in the 
development of Diplocaulus. Their exceptional curvature and 
length are at once striking. Only one is preserved in its entire 
length. This measures 111 mm. Some of the other ribs were 
evidently shorter than this but for the most part they indicate 
an equal or even greater length. 
In the one complete rib there is a departure from a straight line 
of 20 mm., perhaps the average. Some are more sharply curved 
and others less. The distal half is essentially straight, the curva- 
ture being a gradual bending of the proximal half. The curvature 
is within a plane that departs little from the horizontal so that 
a body cross-section shows but a slight down-bending of the ribs, 
a condition entirely in keeping with the generally accepted con- 
ception of a broad, flat, bottom-living type. The capitulum and 
tubercle are both markedly expanded and undoubtedly formed a 
firm attachment of rib to vertebrae. 
HABITS AND RELATIONSHIPS 
The aquatic adaptations of Diplocaulus have been repeatedly 
pointed out by various writers. In typical forms there is much 
evidence that these amphibians were of the groveling, bottom- 
living type. So bizarre are the skull modifications and body form 
and so obscure are the stages leading up to this condition that any 
suggestions are of exceptional interest. 
In several respects the form herein described seems to represent 
an.antecedent step in Diplocaulus evolution. At least it offers 
some pointed suggestions as to the several stages through which 
tTOD. cit. 
