56 M. G. MEHL 
in size and strength of attachment and the vertebral column lost 
much of its vertical rigidity through the reduction of the spines. 
Naturally the supports for the dorso-median fin degenerated to 
a smaller size and a single articular facet. Very likely in the 
process of flattening the body, one of the first steps was the back- 
ward twisting of the curved ribs, a stage preserved in the present 
specimen, and a later tendency toward straight ribs. 
Of the distinctness of this form there can be no question. True, 
the skull differs very little from many described forms. Greater 
variations are undoubtedly rightly included in a single species. 
One might logically expect that the remarkable modifications 
should reach the skull and limbs before the vertebral column. 
While all indications are that the skull and associated vertebrae 
are of the same individual there is, nevertheless, a possibility that 
the association is of two widely differing species. For this reason 
the vertebrae and long, curved ribs are considered typical of the 
new form which the writer wishes to designate as Dzplocaulus 
primigentus. 
The material on which this form is based is No. 564 of the 
Walker Museum Vertebrate Collections in the University of 
Chicago. It was found by Mr. P. C. Miller in Baylor County, 
Texas, on Brush Creek near Seymour. 
The writer takes this opportunity to express his appreciation 
of the kindness of Professor Salisbury in permitting the study of 
this material and for the courtesies shown by Mr. P. C. Miller, 
whose skill and painstaking care in preparing the bones have 
made it available. 
