624 STUDIES FOR STUDENTS 
lower surface of the quadrate shows two parallel notches that 
accommodated a double condyle on the lower jaw. This abso- 
lutely prevented any lateral movement of the jaws in mastica- 
tion. Not the least peculiar thing about the animal was the 
enormous extension of the neural processes of the spine; these 
were long and slender, becoming nearly as thin as a whiplash 
at the upper extremity. They sometimes reached a length of 
nearly three feet, as much as twenty-eight times the greatest 
diameter of the supporting vertebra. The limbs were short and 
stout, but from the location of the articular surfaces it seems 
that the legs were permanently bent, and that the animal could 
not raise itself from the ground. It is probable that it dragged 
itself along after the manner of the crocodiles. It is difficult to 
say what the appearance of the animal may have been. It is 
pretty certain that the immensely tall spines were clothed with 
at least a thin covering of muscle and skin, and then there would 
have been simply a tall dorsal fin that extended the whole 
length of the body. The tail of the animal was long, and the 
feet were strong and provided with claws. The whole brute 
could not have been less than eight or nine feet long. 
Clepsydrops is a much smaller genus, known from the Permian 
of eastern Illinois and Texas. In general features it does not 
differ from Dimetrodon as far as the skeleton is known. It did 
not exceed a length of two or three feet. 
Naosaurus can be told from Dimetrodon by the fact that the 
spines are not only elevated far above the bodies of the vertebre, 
but are supplied with cross-bars like the spars of a full-rigged 
ship. The spines are larger and heavier than in either of the pre- 
ceding genera, and are marked with shallow grooves that indi- 
cate the position of blood vessels, showing that they were cov- 
ered with a layer of muscle of some thickness. Besides its 
occurrence in the Permian (Wichita division) beds of Texas, this 
genus is known from the Permian (Gaskohle) of Bohemia. The 
specimens from the latter locality indicate a smaller form, about 
two or three feet long, while the Texas specimens belong to ani- 
mals nearly or quite as large as Dimetrodon. 
