NO. I.] THE SKULL LV THE MOSASAUIUD^. 21 



this number. In some forms there was an tnerease of this 

 number {Doliehosaurid<B, VaranidcB, MosasaundcB), m others a 

 decrease {Chamceleontida). 



That the Dolichosaurid^ are not ancestral to any ot the 

 lar-er o-roups of the Squamata is absolutely evident. From all 

 that we know, it seems to me that the Dolichosaundee are 

 related to the Anguid^ or Varanid^ ; but so far it is impossible 

 to determine the exact position of the family. , , , ^ 



After having given reasons why the classification of Mr. Bou- 

 lenger cannot be accepted, I have to return to the Mosasauridae. 

 Since Mr. Boulenger's diagrams of the evolution of the limbs 

 of the Squamata are of no use, we have to examine the ques- 

 tion whether we can imagine "that limbs so strongly speciahzed 

 as those of the Monitors can have been modified mto the paddles 



of the Mosasaurs." -r , n ^ io^^ 



I do not see any difficulty here whatever. In the first place, 

 I do not believe that the limbs of the Monitors are more 

 specialized than those of other Squamata, or even the Rhyncho- 

 cephalia (at least in regard to the phalanges) ; and I have no 

 hesitation to assume that unguiculated limbs can be transformed 

 into paddles with numerous phalanges. If we examine, for 

 instance, the Testudinata, we find many instances that the end- 

 phalanges have been modified, that the nails have disappeared 

 (Pinnata, Trionychia, Carettochelyid^), and that in some (Tri- 

 onychia) even the number of phalanges has been increased. 

 That all these more or less paddle-shaped forms of limbs have 

 developed from true unguiculate limbs, there is no doubt. In 

 the Sirenia we find an increase of phalanges and the absence 

 of ungues ; but nobody doubts to-day that the Sirenia developed 

 from unguiculate land-mammals. The same is true for the 

 Cetacea Therefore I do not see any difficulty m assuming 

 that the Mosasaurs developed from unguiculate Lacertilia, 

 which were very close to the Varanid^. To express this 

 affinity, I placed the Varanid^ and Mosasaurid^ in a super- 

 family, the Varanoidea. By this I wanted to say tha the 

 Mosasaurid^ cannot be separated from the ^^ue Lacertiha to 

 which the Varanoidea belong; in other words, that they can- 

 not be placed as a sub-order of the Sqrcamata, but have to be 

 placed among the sub-order Lacertilia. In this opinion I have 

 nothing to change. 



Worcester, Mass., December, 1891. 



