THE BONES IN TUK KNALIOSAURTA. 311 



no malar, quadrato-jugal, supraquadrate, or postorbifcal bones. 

 There are no palatal nares. There is no basioccipital ; and the 

 articulation with the vertebral column is formed by the exocci- 

 pital bones. And the quadrate is embraced exclusively by the 

 pterygoid and squamosal. The anterior nares appear to be sur- 

 rounded by the premaxillary, maxillary, small nasals and large 

 frontals. The frontal bones, however, may as probably be the 

 prefrontal, in which case it would be intelligible that the bones 

 external to them should unite posteriorly with the parietals, being 

 postfrontal bones. The lower jaw is almost entirely made of the 

 dentary bone with an articular element behind, and a long angular 

 or coronoid or opercular element on the inside. 



The vertebral column has nothing in common, except that in 

 both the centrum is biconcave. But in the Amphibians the 

 centrum is long, the neural arch is depressed, the zygapophyses 

 are nearly horizontal, and there is no neural spine. There is no 

 atlas ; and the axis has an odontoid process, the odontoid process 

 reallj being the basioccipital bone. There are transverse processes 

 given off from the combined neural arch and centrum ; they are 

 sometimes grooved, so as to have two articular heads for a rib ; they 

 are always directed backward, and are often long. These trans- 

 verse processes are continued part of the way down the tail. 

 The caudal vertebrae have chevron bones anchylosed to the under- 

 side of the centrum. In all these characters Amphibians differ 

 from Ichthyosaurs. 



The ribs are altogether dissimilar, except that they have two 

 articular heads ; for they are always very short, and do not con- 

 tribute to enclose the viscera, but are directed horizontally outward 

 and backward. 



The pelvis is not like, there being no pubis ossified, and the 

 ischium being a greatly expanded plate in no respect like the 

 ischium of Ichthyosaurus. 



The pectoral arch consists of a combined scapula and cora- 

 coid ; but the bones do not meet mesially. The scapular portion 

 is made unlike the scapula of Ichtlujosaurus by its great width at 

 the line of union with the coracoid, due to forward outgrowth, 

 which makes the anterior margin deeply emargiuate. The cora- 

 coid portion (which is not distinct) has neither the anterior nor 

 posterior emarginations which characterize the coracoid of Ich- 

 tlujosaurus. 



The limbs are totally dissimilar. 



LTNN, JOUBN. ZOOLOGY, VOL. XIT. 23 



