310 PROF. H. G. SEELEY ON SIMILITUDES OF 



scapula and coracoid are not dissimilar ; but in Hatteria the co- 

 racoid has no anterior emargination, and the anterior margin of 

 the scapula is not straight. The clavicles do not meet mesially, 

 but unite suturally (as in some Ichthyosaurs) with a crescentic 

 transverse bar of the interclavicle, which is closely united with a 

 large pentagonal sternum and so far is unlike that of Ichthyosau- 

 rus ; a large cartilage, however, extends the coracoid to meet both 

 its vertical and transverse parts. 



The pelvis is dissimilar ; and the limbs are not comparable. 



§ 8. The Ojahiclian Characters of Ichthyosaurus. 



It were difficu.lt to iind any character of structural importance 

 in common between these types. Prefrontal and postfrontal uith 

 an anterior division of the postfrontal, called the supraorbital 

 bone, combine to exclude the frontal from the orbit in Python ; 

 but the nasals are small and the parietals single and long. 



Nor is the correspondence close on the palate ; for, besides 

 all the bones being loose in serpents, there is a transverse bone, 

 the pterygoids and palatines both carry teeth, and, though the 

 palatines are separated in front by the vomers, the pterygoids 

 are not prolonged forward between the palatine bones and vo- 

 mers as they are in Ichthyosaurus. The pterygoids, as in 

 lizards, meet tubercles of the basisphenoid, and then diverge 

 outward and backward to the quadrate, and do not lap round 

 the basisphenoid as in Ichthyosaurus. The lower jaw, too, is quite 

 dissimilar, its anterior half being made up by the dentary bone. 



In number of vertebrae serpents far surpass Ichthyosaurs ; 

 but the vertebrae have no character in common, serpents having 

 the centrum much longer, procoelous, with one long tubercle 

 for the rib, with the neural arch anchylosed to the centrum, a 

 short neural spine, and a zygosphene ; in the tail there are trans- 

 verse processes and hypapophyses, — all of which characters distin- 

 guish the vertebrae of serpents from those of Ichthyosaurs. 



§ 9. The Urodelan Characters of Ichthyosaurus. 

 The urodelan skull in the Hell-bender, Salamander, or Triton 

 is not like that of Ichthyosaurus ; for the palate is closed by a 

 bone (parasphenoid) which divides the pterygoids and meets the 

 vomers, which carry teeth. In Ichthyosaurus this bone does not 

 exist. Then in these animals the orbit is confluent with the 

 temporal fossa ; and the space is not circumscribed, there being 



