SAMUEL WENDELL WILLISTON 687 
on Permo-Carbontferous Vertebrates from New Mexico. The same 
year saw the publication of his important papers on the primitive 
structure of the mandible in amphibians and reptiles and on the 
skulls of Ar@oscelis and Casea. The close resemblance of Arcoscelis 
to the Squamata especially in the temporal region was noted. 
Early in 1914 came the publication on Brozliellus, one of Cope’s 
“batrachian armadillos,” and the fuller description of the osteology 
of Ar@oscelis, with a discussion of the relationships of Ar@oscelis, the 
Protorosauria, and the Squamata. He then referred Areoscelis to 
the Protorosauria and placed this order next to the Squamata. In 
the same year he published a series of life-restorations of some 
American Permo-Carboniferous reptiles and amphibians. 
His principal publication in 1914 was the book on Water Reptiles 
of the Past and Present, in which his life-work on these animals was 
admirably combined with the results obtained by other workers. 
Williston had shown a bent for the harmonious study of form and 
function, of structure and habit, of environment and adaptation, 
which he applied with skill and originality to the interpretation of 
the highly diversified forms of aquatic life. He followed Eberhard 
Fraas, of Stuttgart, in making a special study of aquatic adapta- 
tions in the vertebrates; consequently his book on the water rep- 
tiles constitutes one of the most important contributions which we 
have upon this subject. 
The year 1915 produced his papers on Mycterosaurus, a very 
interesting reptile, that threw light on the origin of the diapsid 
types, namely of reptiles with /wo arches at the side of the temporal 
region of the skull. Also on Zvrimerorhachis, perhaps the most 
archaic of the American Temnospondyls, or amphibia with the ver- 
tebrae composed of several pieces. In 1916 he published the careful 
description of the skull and skeleton of Pantylus and of Thero- 
pleura, together with the important discussion of the origin of the 
mammalian and reptilian types of sternum. This paper was 
followed by the admirable Synopsis of the American Permo- 
Carboniferous Teirapoda, in which the principal types were illus- 
trated, and careful definitions of the various groups were given. In 
1917 he began a general work on the Reptiles of the World, 
Recent and Fossil, wpon which he was actively engaged up to his 
